Since I am thinking about investing in this sector I would like to find a resource that can show me all of the vacant box stores waiting for a new buyer?

Agreed, find a buyer’s agent to suvomit your offer.  

I gave the buyer more money (through offer and interest income), but I saved almost $10k cost to me, with higher CF, in the process.

After all contingencies have been met, buyer will get primary position, assuming no other buyer's have met this criteria before them."

Does it fall to the seller or buyer?

All information in listing should be verified by buyer prior to purchase..

Also, the association controls finances, insurance and many other things, a friend of mine has a condo in a unit mainly controlled by Canadians that are seasonal, in their infinite wisdom they decided to not maintain flood insurance for the development (they are in a flood zone)  now the units are unfinanceable , so the values are lower because only cash buyers can buy in the building.

Subject to Buyer obtaining any and all permits required for building two single family homes on lots 1A and 1B."

Any advice on finding 1031 exchange buyers or sellers?

Just see how they respond, maybe you get your price.Would you still want to stick to your "original plan" if this buyer was willing to pay you 30% more than you think the current value might be?