The Wireless adaptor or the link cable? If it is the wireless adaptor you can get it for about $20.00 or go to nintendo's online store at www.nintendo.com
Oh the AC one? tou have to buy another GBA to get it because IT is NOT sold seperatly and who knows why I don't know but you cannot get another one without buying another GBA SP. Would you like me to add you to my buddy list? I will be glad to add you.
They stopped make ing the regular GBA because of the SP's popularity and the accessories for that system are harder to find but you can still get them. I am not sure if www.nintendo.com still has the or not but check their online store or check your nintendo place in your area to see if you can still get the accessories for it. Go get sp because it is more like a regular game boy style or get a micro.