I've been buying mine at Home Depot or Lowes.
At the Home Depots I've bought them at, the brand name is GE. Model number FXWTC rev.2
At Lowes, it is Whirlpool. Model number WHEF-WHWC.
If I recall, they're about $8 or $9 for a package of two and can be found in the section where they sell house filters. I think the one at Lowe's is a dollar cheaper. You'll see canisters that look similar to the ShurFlo that are found in some of the Winnebagos (like mine, an '07 Meridian). These all take a standard cartridge that are interchangeable among numerous filter canister manufacturers. They all look alike, are the same dimensions, have just about the same specifications, and are carbon paper activated.
They are interchangeable with the ShurFlo RV-10C1-A.
Here's the one from
Home Depot (prices online are more than at the store).
Here's the one from
Lowe's (prices online are more than at the store).
edit: The reason I started buying them at HD and Lowes is that they're half the price of the OEM found at Camping World. At CW, they're $9.99 for one and have the same specs (all probably made at the same manufacturing plant in China
:
http://www.campingworld.com/shopping/item/waterguard-carbon-paper-water-filter/34009