I think what some agents are missing here is that you've said "NOT ON THE MARKET". If it's not on the market in any way, shape or form, then it's not for sale. The seller would have to be willing to go through the short sale process, and since it's not on the market, one might safely assume that the sellers are NOT willing to go through the short sale process.
Another factor here is that some loans backed by government programs are not allowing short sales during the redemption period. So, that might also be the factor that's at play here.
Good luck and let me know if you want to pursue looking at some properties. No strings!!!! :)