Interesting project!
For a filtering solution, which may be more likely than a coating solution, I believe that most window tinting is actually
UV blocking so might not be what you seek. UV bandpass filters are available, but really expensive. The inexpensive filtering solution for many projects, Rosco gel filters, appears to be a no-go in this case. What a shame. It seems that UV photography wasn't intended to be easy for the masses...
BTW, just for education sake and fun I searched for those dyes in the recipe posted by
@Kino. Can be procured today but at considerable expense.
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Have you thought of applying for a grant to pay for this?