If you mean the bowl type strainer rather than a filter that fits on the pump inlet?, then any caravan shop should have one. They are common to all/most internal pumps so the threads are the same.
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets