At a recent Ar15 shoot I managed to lose two pf my covers for my Magpul mags. They are available from Brownells but losing them bites! So here's how I solved the problem.
I you will notice the large hole in the bottom of the spring assembly. I used that as an anchor point for a tether.
What you will need: Magpul Magazine, parachute cord or something similar or some nylon string, scissors, flame producing device.
Cut a piece of the paracord about 12" and remove the inner strings. Burn both ends to prevent unraveling.
Tie the cord or string to the cover
Slide the base plate of the magazine back until the hole is exposed and put the end of the cord or string into it and close the cover. If you melt a large enough glob of nylon the cord will hold fine by itself otherwise tie a small knot at the end of the cord.
Your finished product should look like this. No more lost covers!!