Old mast: weird size

Knowledgeable windsurfers! I have come into possession of an old mast made by a company called…Windsurfer! It has its own mast extension with some weird-ass extension that isn’t US Cup or Euro compatible. I want to get a new extension for this mast but the inner diameter is a wonky 44mm. Too small for any SDM and too big for RDM. This is for a slightly silly project so I don’t want to break the bank but can I get an extension with a non-standard diameter. Thanks in advance and sorry for the noob question!