I didn't find any cartridge's with Ram-Expansion on that page you recommended, but I'm not in need of one so it doesn't matter for my sake.
But they did have an Arcade Racer! Gotta buy two of thoose some day.
GoCyberShop
Have the Saturncontroller and Action Replay Pro. I don't know the exact specifications on the PRO-version, I've got the PLUS myself.
Metal Slug only requires (SP?) 1 MB-Expansion, but the AR PLUS has an autoswitch for it, and I GUESS the PRO version does too, but maybe you should wait for someone with more info to post, or try to get the info by yourself.
Lik-Sang
Also has controllers, no 3D-controller like gocybershop though, but the official Arcade Sticks!!! I was going to order them as soon as they got in, but the damn shipping is more expensive than the controllers! (That's because they weigh 3.2 Kilos, it's pretty reasonable shipping for lighter pakages, like a RAM-Cart and a normal controller for instance.)
I'm just hoping they still got the Arcade sticks this fall, because that will be the next time I will have any money to spend.