I have a few cards that I've been looking for for a very long time:
1994 Fleer Ultra had two insert sets specific to retail boxes that were one per series. These are hard pulls at one per box.
I need the RBI Kings Matt Williams...I've actually never seen one up on ebay.
I also need the Andres Gallaraga On Base leaders. One came up on ebay for the first time in a few years. I put a snipe over $10 on it which I thought was an insane price, but I wanted the card and I figured its worth $10 to cross it off my list for so long. The one initial bid had a max bid higher than that. Go figure
The other really tough ones...and I'm not sure that they were even made...The company Signature Rookies had some really nice insert sets of HOF's and sports heroes of various sports...in particular their Gold Standard set, and the Tetrad Titans insert sets. For those that don't know, SR went down in flames sometime in 1996-1997 because the CEO Tim Flatt was into some shady business practices. However, I do believe most, if not all, of their autos were authentic. Lots have found their way into TPG slabs as authentic. I do know that one of the shady business practices is that the owner or someone close to him absconded with autos that were supposed to be redemptions from packs.
So I assembled the Tetrad Titan from 1994 without too much difficulty, and for not much money. Includes autos of Bruce Jenner, Larry Holmes, Bobby Hull, Bobby Allison, Larry Bird, Isiah Thomas and some other olympians. Also an infamous OJ Simpson auto which I do, and will not, ever own. The 1995 one is only a 5 card set. 3 were easy and inexpensive for what they are...Dennis Rodman, Kareem Abdul Jabbar, and Katarina Witt. The last two...well I don't remember ever seeing them on ebay...
Bob Griese
Roberto Duran
I'd love to own these(if they actually exist). The 1994 ones are nicer and feature easier to read autos.
FWIW, there was a near impossible set of cards to get...the Kromax product had an insert set of 5 autos of all star NBA players..Dominique Wilkins and Tim Hardaway had productions of around 1000. Those pop up on ebay every now and then. However the Scottie Pippen I believe is numbered out of about 30, and the Charles Barkely and Patrick Ewing are numbered out of 5. Those came up a year or two ago on ebay and I think went in the $350-400 range.