Based on this product's specifications, here are some alternatives and similar models
Lens cap PENTAX O-LC49 49 mm for 49mm front threads
Summary description:
PENTAX Lens Cap O-LC49 is a 49 mm front cap designed to protect the front element of lenses with 49 mm filter threads. Simple snap-on design ensures secure fit and easy removal. It prevents dust, scratches and fingerprints during storage and transport and is compatible with PENTAX and other lenses that use 49 mm threads.