There are 3 types of people who hold chips I want (I think):

1. People who have zero intention of letting the chip go (part of their primary collection and plan to keep it forever). These folks generally aren't even advertising they own the chip, much less advertising it for trade/sale.
2. People who would sell for the right price, but only if someone meets their standing above-market price or if someone makes a blind offer first.
3. People for whom the chip is a duplicate, poor quality, or not part of their primary collection who are willing to sell for anything reasonable.

#3 is easy to negotiate. This is the majority of ebay and private sales.
#2 is difficult in the sense that a way above market price isn't enticing (assuming it's firm). Buyer simply has to be the one to move the market higher in order to get the chip.
#1 is the hardest. We all know there are chips in collections, but we only know a few that have them. If they've made it clear they're not selling, then we need to find ways to locate other chip owners and see if they're ready to sell.

The latter is what I'm attempting to do right now. I know, for instance, there's a beautiful Louisiana Club chip on eBay for about double book value. I COULD add that to my collection today, but I'm not willing to come up to that price and he's not willing to come down, either. Stalemate. Fine. Moving on. I do keep finding one or two chips here and there to check off my list (got 3 more in the past couple of weeks). Did I pay more than I wanted to? Yes. Did the seller get as much as they wanted? Probably not. So, that seems "fair", right?

As for how to write up the "future possession" agreement, I agree that it would be difficult and both parties would have to really iron out details with family, attorneys, and use recorded documents to protect both sides' interests. Adding a lot of "what if" clauses and using a bank escrow to hold monies until triggers are reached (seller dies, buyer doesn't receive promised goods) would be necessary. But I don't think it's impossible to do.

All of the above notwithstanding, a simple purchase and transfer today is best. Sooooooo, whatcha got?