Ach none of that! Just make it myself

Pollycarbonate is very easy to work with and mould to the shape you want. Perspex or acrylic not so much as its very brittle when cutting and can snap pretty easy.
Although just re-reading your post, what is it exactly rear window wise im needing? The only bit that is leaking is the edge between the front corner of the side window and the hard top, there is a slight gap their.
I did however make and fit a new pollycarb rear window to my aero hardtop as the last one had holes drilled in it for racing.