Replacmt window supplier?

[Breconeer]

Hi, looking to replace the sliding windows on both sides of our Sheldon Hi-top roof. Existing ones are too corroded/perished to mend (29 years old). They measure about 39" long x 8.5" high, with rounded corners and sliding glass. Could cut the fibreglass roof to accommodate greater length, but not for greater height.

I imagine the answer is somewhere in this forum already, but my search efforts didn't find it. We have someone local who can fit them. Looking for entire frame/glass/seals/handles, not just innards. I see plenty of hi-top vans (and boats) with them, so I presume they are a stock item someplace?

Thanks.