Do you mean in the eShop or whatever? Because I'm pretty sure HHD can be played on a regular 3DS, you just need the reader, and that's only if you want to use the cards.
My purple 3DS is unfortunately having some problems on the bottom screen, so it is looking like I will have to upgrade. I'm having a tough time deciding whether to upgrade to a regular XL or if I should just go all out and get a New 3DS XL.