I am looking for a small tin or sample of dark brown UVPC paint to cover three small bits of my PVC window where birds have picked at the top covering . Would you have anything suitable?

Assuming the UPVC window is clean, dry, sound and prepared you could consider Zinsser AllCoat Exterior (Water Based).

This is available mixed to many RAL, NCS or BS colours in a matt, satin or gloss finish.