It appears EBGames.com is having a clearance sale... one of the items on sale are the Interact GBA Game Cases... these little beauties are about the size of a GB/GBC game, but snugly hold two GBA carts.
(Image stolen)
Before discount, the cases are $3.70 for a pack of 8... after the discount, they are just $1.11 for 8.
http://www.ebgames.com/ebx/product/191570.asp
Enter the coupon code BIGSALE and feel free to order up to ten. The EB description calls them GBC cases, but don't worry. I just got my shipment of ten packages today.
Now I just need 160 more GBA games.

(Image stolen)
Before discount, the cases are $3.70 for a pack of 8... after the discount, they are just $1.11 for 8.
http://www.ebgames.com/ebx/product/191570.asp
Enter the coupon code BIGSALE and feel free to order up to ten. The EB description calls them GBC cases, but don't worry. I just got my shipment of ten packages today.
Now I just need 160 more GBA games.