Could you just cut the top part of a Saiga mag off, and attach it to a G3 mag (or any other 20 rd .308 mag) with its top off? Then you could have a 25 dollar 20 round mag. I know this wouldnt be too easy, but I would give it a try. Since you are trying to attach metal to plastc, a bolt on bracket would be the only way.....hmm.