Filter bodies, filter replacement cartridges, gaskets and seals can all be ordered from klrfilter.com.
The filter base is pretty heavy duty, so if it breaks for some reason it had a pretty rough life. They are closely inspected and functionally tested. If it is defective please return it within the 30 day policy window for a replacement. The filter base is not sold separately from the filter kit.
Each filter body is pressure tested prior to shipping, so this should not happen. The filters have a 30 day warranty. Return everything for either a refund or replacement.
The easiest thing is to run some hot water right along the seam where the body screws into the base. Let it get warmed up then then try again. It should unscrew relatively easily.