I believe you are referring to the sump portion of a filter housing. Here is a link to our sumps page, where you may find what you are looking for, if we have it.
Water Filter Housing Sumps and Whole House Replacement Canisters for Ametek, US Filter, American Plumber Housings In the end, it will probably be easier for you to replace the whole housing.
Thank you,
WaterFilters.NET