Are you asking about replacing just the "glass" in the opening Gray portlights? I don't remember any of the H25s having fixed ports. I do recall that some owners have removed opening ports and installed fixed ports. Maybe that is what you have.
If it is the opening ports that you are wanting to upgrade I have never heard of anyone doing that. The exact replacements are still available:
http://www.pompanette.com/bomar . But I don't think parts like just the hinged opener with the "glass" are even orderable. You could call Pompanette.
A lot has been written about trying to improve the glass. Meguiar's polish is often mentioned. Are you fixing leaks or transparency?