It turned out there was just something wrong with the system. They had to make a custom order form for me.
BTW, PX-Airsoft is awesome. The package arrived in UNDER A WEEK and it was shipped via Hong Kong airmail and not the more expensive EMS option. When I got the box, it had an Xpresspost sticker on it so it was expedited somehow.
Also one of the GBBR mags I bought had a bad valve. They said they had tested them all before but sometimes shipping mags on a cold plane over the ocean will damage seals. I e-mailed them and they are going to mail me a new replacement valve free of charge.