I have purchased actions from individuals as well as some from sales at stores. Though one place that I have found some good deals has been to find a rifle at a pawn shop. Yank the barrel and send it to the barrel-maker of choice or gunsmith of choice and have them put it all together.
I have a 25-06 that started it's new life when I got it from a pawn shop for a steal of a deal (and yes, I check the serial # w/ the PD just in case).