1994 Finest Pre-Production SPs?
 

Finest pre-production cards were issued as inserts in Series II of the 1994 Topps regular set.

In trying to complete a set of these 40 cards, I've noticed there are 4 which seem to simply not be available - Dwight Gooden, Roberto Kelly, Gregg Jeffries and Dante Bichette. I've been looking for them off and on for several years to no avail, while all the others seem to be readily available.

Just the other day I did manage to finally nab a Gooden, which was only the second one I'd ever seen (the first being a slabbed specimen that's been on eBay seemingly forever).

Does anyone know if there are scarcities in this set?

From COMC sold information:
5 Dante Bichettes were sold and delivered at a highest price of $4.50
5 Dwight Goodens were sold and delivered at a highest price of $4.50
4 Gregg Jefferies were sold and delivered at a highest price of $4.30
6 Roberto (Bobby) Kelly were sold and delivered at a highest price of $6.50

So they're definitely out there. Most of the other copies on site had similar numbers of cards submitted, some up to 10 or 12. But from past experience, people will submit more cards of players that have a following, and most of those guys are has-beens with no player collectors. So they may not get sent to COMC or listed on eBay because of perceived lack of demand.

Oh, and I scoured their base cards and just found two additional preproduction cards hiding among them: Gooden and Tino Martinez. So there's another one available that has been sitting on COMC for about 4 years at 50 cents that nobody noticed was a preproduction card. That's another problem with looking for these: most people who collected them would have filed them under the regular set, and only be looking specifically for the refractors if they're going through their collection to figure out what is currently worth money.

As for sportlots.com, none of the ones you mentioned are available at this moment. Some have a bunch of copies for sale, however.
https://www.sportlots.com/inven/invenbin/result.tpl