I purchased one holder a year or so ago with the intention of fashioning an adapter back for my 8X10 camera so I could use this holder to shoot trimmed down X-ray film, with the end result being cyanotype prints.
The holder is (I assume) a plate holder but it came with some DIY inserts so I can shoot film.

Anyway, I have not gotten very far in my efforts (I have gotten no where).

I am sort of rethinking before I even begin and I need some advice: Since I won't be able to buy any (X-ray) film in this format I would have to buy large and trim down. Naturally, I would want to minimize waste.

What size of film, if any, is available for trimming to 8.5X15"?

And if no film will work, is there a B&W printing paper size that would be a good idea to try for making paper negs?

In other words, if there is no manufactured light sensitive material that I could use in this holder, why go through the effort of fabricating a back for my camera (questions I should have asked myself before purchasing the holder in the first place)...