Lots of online shops sell R4. but be careful, too many clones. I boungt a classic R4 DS card from Depot888. Dont want to damage my DS machine with unreliable new product R4 SDHC Card. btw the price is $23.99, with code 280721 can save $2. LOL
I know you can buy the card from www.gameyeeeah.com I bought a m3 ds real from them, and it was shipped to me in about 5 days. I would definitely recommend the m3 ds real over the r4, but if you are set, I can say I used gameyeeeah.com and it was fine
buy the edge ds , m3ds real or cyclo ds evolution they are all much better than the r4ds from here - http://www.dealextreme.com/products.dx/category.604 woof811.