im a little late getting to this one, but heres my 2 cents
if you are looking for a SD converter to drop.gba games onto an SD card and play them in a GBA (not SP\or SP) then yes its possible
http://eng.supercard.cn/download.htmscroll to the SuperCard SD & MiniSD section all of the cards that you see there are what youre looking for, there is a link to places you can buy, the variety of cards there are geared toward the DS now but the section i pointed out is GBA
the good news is if you get a DS you dont need anything but a Passcard to mod it
hope that is what you were looking for or helps someone