That's a fun prompt - other than a sample of Balkan Sobranie that I believe was from the 70s, I think all of the discontinued blends I've had the pleasure of smoking became unavailable in more recent history (I know BS isn't necessarily discontinued, but I guess I'm including past productions of continued trademarks here). That in mind, my answers are more informed by curiosity and whimsy than chasing the smokes of fond memories.

First I'd say Edgeworth Plug Slice. I certainly enjoy a good Burley flake, but a big reason is its connection to Richmond, my city that I have much love for.

Carolina Queen was supposedly Sutliff’s first manufactured blend, probably released in the early 1890s. Not even sure what style it was, but if the name’s reference to the Old Belt is any hint, probably bright leaf. I'd be interested to try that for sure.

Kinda at a loss for a third. Capstan Original Navy Cut is one of my favorites. I'd be very curious to taste the original recipe, so I’ll go with that. 

I certainly romanticize things from the past that are gone and also desire things I can’t have and there are tobaccos that fit into that category for me. But if I’m honest with myself, most, but not all of my desire for old blends is from nostalgia more than their lost quality. Three that I can think of that were special though that I would buy in quantity if I could were one you mentioned, Three Castles. There are many tobaccos available that are close, but none quite the same. Murray’s Erinmore Flake and Mixture, the current iteration is not bad, but it’s a shadow of the original. Lastly, the old Gauloises Brunes. I’d buy a pallet of them if I could. 

If I’m being objective though, right now is actually the best time ever for pipe tobaccos. There are more choices of quality blends available now than ever and with the internet, it’s possible to find them all. I remember a time when Samuel Gawith and Gawith Hoggarth products were almost mythical since they were nearly impossible to find. Not like waiting for the next shipment to arrive at whatever website you buy from impossible, but like you just couldn’t get it. Now I have access to everything they make. Also, the majority of the “old” tobacco was a mass produced product. It was much more “one size fits all”. There wasn’t much in the way of truly unique or small production blends available and I find many of those to be extremely fun today. 

I started smoking a pipe in 1973. It was then I was introduced to Elephant and Castle. The Stout and Cromwell. Exquisitely delicious. As a side note, I wonder if there were 2 Elephant & Castles. Because I found information online about a company formed in the 1980s. But I was buying the same blends in 1973! And shortly after I started my tryst with Lady Latakia, Elephant & Castle sold out to the Germans. 

So imagine my surprise to see the same blends from an E&C created in 1981. I was not smoking a pipe at that time, so I would not have purchased any of their tobacco. Yet I still have a tin of The Stout and one of Cromwell.

Tis a mystery.

Back to the topic at hand. Elephant and Castle The Stout. Delicious stuff.

For a second choice, I'm thinking the original London Dock. My grandfather smoked London Dock and I always liked the spicy aroma. I smoked the Middleton version in the 80s and liked it. But the blend had apparently morphed into something a bit different than the original. Blends have a habit of doing that when companies sell out or are taken over.

My third choice is a toss up between the original Lorillard Briggs Mixture and Douwe Egbert's Amphora Rich Aromatic. The blends are polar opposites. Briggs, with only a whisper of topping, is essentially a non-aromatic. Amphora Rich Aromatic, by contrast, is a delicious Dutch Cavendish as only the Dutch could make. Strong aroma and taste that is the utmost in the pleasure department. I can't make up my mind. But either of those will do for #3.

Fun exercise. The past, though, is past. And we are lucky for all the choices we have in the present.

Balkan Sobranie Smoking mixture

Balkan Sobranie 759

Dunhill London Mixture

Middleton's London Dock

Dunhill Durbar of the old days. Available only at Dunhill store in London. 

Compton's of G - Balkan

McClelland - Tudor Castle

McClelland - Yenidje Supreme

and I old enough to have smoked -- a few times -- the original Balkan Sobranie of London - cutter tin, white can.

Edgeworth Sliced

Dunhill London Mixture

Reading reviews of Dunhill MyMixture 221B Baker Street make me sad that it is gone. Even the match version made by Robert McConnell, Barking Road, is impossible to acquire in the USA (though if anyone has a vendor source, I'm all ears!).

Mick McQuaids. Didn’t realise it was discontinued… very sad to find this out as it was always my go to daily smoke. Just bought out a stock from my local shop. Only had 6 packs left oh well.  

I recently smoke a tin of Marcovich Black and White. It is english made and from the 80's I think. Excelent condtition and  a marvelous smoke. The latakia is a litlle muted with time but as Pipestud mentioned a great and stout blend in the english vein. I easily can imagine it back on the shelves of tobacco stores

Is there anybody who has smoked Marcovitsch's Black and White and loves it too? 

The old english made latakia blends are great and the maturing is a big part I know. I had the opportunity to buy 5 tins of Wellauer Best and one English Blend, In this condition, after 23 years in the tin, Wellauer Best is my dessert island blend!! If anybody can buy an old   tin,do it!!  No regrets I swear