if so, how where?

you can from other users. Either search up the credit cards (100, 250, 500, etc) in the shop search, which will show you all the ones for sale, or you can make a forum topic asking to buy in the wanted section of the advertising forums. There are also constantly CSC sale topics, so watch out for those as well :)

Also, be prepared to shell out between 8mil sP and 35mil sP in some cases and depending on the day.

The actual name of the item to look for is "Credit Gift Card"

examples:

thank you!