Truman, you may have a little bit of an issue selling your magazines.
Cheaperthandirt.com has the steel 20 round surplus magazines for the H&K 91/G3 (SAR-8 and others) going for $2.97 and the aluminum 20 round surplus magazines going for $1.97 as of this moment (10/8/12).
Yes, you have to factor in shipping and handling if you buy from them but that's not really a big deal - especially if you're already picking something else up too.
Back in the day they were selling the aluminum magazines for $0.99 each and, well, you know how it goes - how can I NOT get magazines for under a buck?!?
I picked up more of them than I should have and now I've taken to letting them go to friends and family who might need them gratis and to people who answer my online ad for cost ($1) each.
I hope you sell your magazines but I thought you and everyone else might like to know what they're going for on cheaperthandirt.com (though I personally prefer Midway on most things I purchase).