I thought it might be a Unicel number since they mostly all start with a C but I could not find it listed. Is this a free standing cartridge filter or a skimmer filter unit? If you could post the model number and make of the filter itself it would be very useful. I have several different crossreferences at work and might be able to find what you need. Also post exact measurements of the length, diamter of the end cap, diameter of the inner hole, and whether there is a support tube inside or if the pleats are exposed on the inside.

Edit: if this is from the Hayward simmer with filter in it they have discontinued this but it might be available from one of the third party cart manufactuers like Unicel, WorldPool, or Pleatco.