I recently ordered one. Shoptemp had a few listings, and nds-card.com was the most promising of the bunch with the better shop reviews. It was $23 shipped via tracking from China and they had it mailed out quickly. They DO take Paypal as well, but you have to place the order and then email them for the PP details after, it's a bit awkward but they're trying to keep PP info secret to avoid getting it closed for selling flash cards.
Whichever shop you go with, they tend to offer SD cards with them but I wouldn't bother with that bundle deal. You have no guarantee the SD card will even be genuine, and their prices are rather high. Walmart is selling the Samsung EVO 32GB card for $10 and Best Buy carries the EVO+ 64GB for $20 or less.