Have a look at some websites that sell hair system supplies and look at what UV protection conditioner sprays they have.
A good website to look on is Treat Project, run by someone who used to part of Hair Direct:
https://www.treatproject.nl/product-category/care-products/
They ship worldwide and stock several different UV protection conditioner sprays. A suggestion for you (which I've tried myself):
BonfiRemy Silk Mist Leave-in Conditioner 8oz strengthens human hair replacement systems and protects them against UV damage from the sun.
www.treatproject.nl
The Pro Touch leave in conditioner was pretty good too.
If you're in the UK, you might try these:
A long-standing industry staple, this B5 conditioning spray will help maintain the condition of your hair. It also has a sunscreen, to prevent colour loss whilst soaking up the rays.
hairhub.com
Leave in Conditioner from Walker Tape Co. gently moisturises and detangles wigs and hair hair systems - simply spray on as needed.
www.holistique.co.uk
Pro Series Leave-in Conditioner for Hair Systems. Smooth, healthy and shiny hair with complete protection from daily strains and UV.
www.holistique.co.uk