I Got those mags you are talking about from AirsoftGI.
Ask them if they can ship your order using USPS. Can't rememeber if they said "yes" but there's nothing to loose.
For the mags ; Fits perfectly in my G&G GR-16 and my Classic Army M15. Feels very solid. Color is very cool. And I think they are really close de RS mag dimension. And those mags are king because of the long follower that really pushes ALL the BBs in. So there's really no leftover when you remove the mag. They also feed very well.
Only downside ; when you carrying all of then in your vest, it's getting really heavy. Also, the spring that pushes the BBs inside the mag is a bit too strong. Might not be the case for you but when I fully load my mags and load it in my AEG my first 10 shot a really shit. It means that there's so much pressure made by the spring in the hop-up chamber that all my BBs are kind of stuck in my hop-hup chamber. Solution ; do not fully load your mags and everything will be alright. Might need to find an other solution right now I'm okay with it. Also, I alreay had a problem with the base-plate screw holding the frame and the mechanism ; the plastic where the screw goes broke so the mag wasn't holding together. But some glue and you're set.
I hope it's okay