Hey deer hntr, try AuctionArms or GunBroker on a regular basis. They show up from time to time in lots of three to five at about $5 a wack. Picked up five a month ago to rebuild some factory tried and true, well tired and deblued.
They are listed under "magazines" or "other rifle parts".
As a tidbit of steel floorplate info. I have found two types of the securing dimple;#1 has the large half moon dimple that we see on newer pre-bans. #2 has a deep narrow channel running from the center of the floorplate hole to the outter edge. Two of the five I picked up were of the second type. All measured out the same with a digitial caliper and all had the Ruger Mini 14 logo. Different era, manufacturer, counterfit? Beats me.