do you mean like a little thing that sits in the intake of a cainster filter and takes out larger particles. a pre filter.umm i think most eheim classic (2217, 2215) have them, but they are and extra.
Just go to Petco or Petsmart and buy a sponge filter for a powerhead, then stick it over the inlet on the canister filter. Thats what i did when i was using a Toms Rapids canister on a little 10g breeder tank and it worked like a charm and only cost me like $3.