I’ve started to look through wartime pictures for painted helmets and I’ve found a few.
Theres a good collection of pictures on MosinNagant.net also.
The most famous painted helmets are those with the “skull” type markings, they seem to have been used by the Kev. Os. 4 light detachment and possibly by the Uusimaa cavalry regiment.
A good overview of helmets in finnsh use: Pottia.net