Here's the deal.
What you want is to buy a mag body, floorplate, and follower that are in good mechanical condition.  The new spring is great, but tells me that maybe the old ones are worn out, and thus the mags have seen some use.
No problem.
Here's what to do:
Disassemble the mags.
Clean them inside and out using a degreaser such as Simple Green and hot water.
If the mags were painted, strip off the paint with some chemical stripper, following the directions.
Wash again, thoroughly.
Dry and inspect for mechanical condition, especially the feed lips.  Compare the used mags to the one received with your rifle.
Wire brush off any light surface rust.
At this point, you hopefully have some clean mags with most of their parkerized finish left.
You can leave them as is, lightly oil them and re-assemble with the new springs.  You can blast them, and re-park.
OR, you can de-grease them with acetone or somesuch and paint over the remaining park with Brownell's aluma-Hyde II epoxy paint.  Properly done, epoxy paint over parkerization is a VERY tough finish, superior to either alone.  Follow the instructions on the paint can to the letter, and wait a week before handling.  No kidding about that.  Resulting assembled mag, with new spring and paint over park finish is better than new.

DSA's customer service is first-rate, so any mags you receive that are mechanically N.G. will be exchanged, I'm sure.

Tapco also sells mags.  Some folks have a beef with them which concerns another board, but aside from that, I've had no problems with their merchandise or service in the past.