My building has same issue, last four sales have been cash to avoid these types of issues. The Credit Union is a good idea.

But first I want to know did you approach Sponsor who owns 51% maybe he would be interested in buying.

Second. My building allows subletting and renters. AKA investors. Investors unlike primary home owners often buy cash. Higher rates for investors and lots of headaches. Does you building allow subletting? Are there restriction? Given we sell units that way in my building if the unit is in a decent location and maint not to high I could pass the info on to the investors.In fact one guy is looking for a coop with liberal renting rules which is hard to find.

Also did you post an ad in buildings laundry room or something. Sometimes folks in building are more likely to buy. Lets say Mom is getting old and kids live in building already. Folks trading down often have cash. Many years ago when I lived in a coop when mortgage were hard to get in 1992 folks in neighborhood trading down from a house to a coop often bought cash.