I really need to get one to enter the pal park.
Yes, you can still buy GBA games. Most places do not sell them new any more (since they are not being produced) but you can get them second-hand.
Amazon and eBay are usually the best places to go.
If you don't want to use the internet I suggest a store like GameStop or EBGames that sell used video games, however the internet would have the widest selection.