Recently many of the online shops who stock the DS/DSi/3DS Flash Carts have gone out of buisness, but luckily a new shop called CoolGadgetsGifts has opened which stocks most of the best brands that we use for homebrew on our DS Consoles.
Including these
Acekard 2i
R4 DS
R4 SDHC
R4i Gold 3DS
R4iDSN 3DS
R4i SDHC 3DS
DSTT / DSTT i
iSmartDS Premium
R4i SDHC V1.4.2
M3i zero
iEDGE