Regent is, or was the WalMart house label for Marineland products, including your filter. Or, it's no longer being made and WalMart simply dropped carrying the cartridges, but the best source of information might be the mfg. at:

http://www.marineland.com/sites/Marineland/CustomerService/ContactUs.aspx?id=1814

Also- check out any large online seller of aquaium products. BigAls.com is one the better ones and has an 800 number for you to call, to be sure the cartridge they sell for the compatable Marineland filter will fit your Regent, and it should.

I have both a Regent hood and 6 gal. tank and both are identical, including all parts as well as cartridges, to their Marineland branded counterparts; the Eclipse 1 hood and Eclipse System 6.

Also, if the cord on your filter still has the small label on it, down near the plug; check it out. Both of my "Regent" products have Marineland labels on the cords, with model code numbers on them, which if yours does; might be your best lead to identifying the Marineland branded filter identical to your Regent.

Good luck in your search.