Oh! Search local feed stores- not the big chains. I find MANY have chicks, and they rarely have minimums. A query on a local chicken FB page night help answer that, too.
I just ask my TSC manager. They'll sell me any number of chicks because they know that I know chickens. If you explain the sitch, they might allow you to get just 1.
Otherwise, hang out by the bins at the store for a few. Someone will come in to buy chicks, and you can pay them to add one to...