Any flashcart that works on 3DS works on the 2DS, from what i've read, r4i gold 3ds card is the best flashcart for 3ds and 2ds out there, here you go http://www.r4flashcart.com/8-wood-r4i-gold-3ds-flashcart-for-3ds-xl-3ds-dsi-and-ds-lite.html
flashcarts which can work on the 3ds will be also working on the 2ds, so currently i recommend you buy r4i gold 3ds card for your 2ds console. check here: http://www.dsflashcart.com/r4i-gold-3ds-wood-r4i-3ds-flashcard-for-ds-dsi-3ds-p-248.html
If you check ,you will find N2DS has almost all function of N3DS, that's to say,flashcart that can work on N3DS will work on N2DS at the same time. If all you want is playing nds games or homebrew, then you can buy http://www.modchipfactory.com/wood-r4i-gold-3ds-flash-cart-for-3ds-xl-3ds-dsi-and-ds-lite-p-1.html , this card support almost all latest nds games.
2DS Factory Version is v6.0, any flashcart which work on 3DS v6.0 also work on 2DS v6.0 perfectly. dstwo, r4i gold 3ds, r4i sdhc 3ds..
I think the choice should be between r4i gold 3ds rts card ( http://www.digimartz.com/r4i-gold-revolution-for-3ds-ds-dsl-dsi-v144-freeshipping_p741.html ) or supcard dstwo . Though many other cards can also support 2ds but r4i gold 3ds and supercard dstwo do great job on updating.
