I don't think there are lens caps for the male end.
What I would do is buy a filter stack cap set of the appropriate size and use the female one. https://www.amazon.com/Fotasy-Metal-Filter-Stack-Aluminum/dp/B005B8M19O/ref=sr_1_3?dchild=1&keywords=49mm+filter+stack+cap&qid=1615506882&sr=8-3