I have the non-blowback Umarex P.08, and after looking at a bunch of wood grips, I realized that none would fit without major alterations. So I also went with the paint route - but in addition to paint, I also used alcohol ink, which you can use to give a really decent wood grain appearance. Here's the process:
-- get a set of brown alcohol inks - I used these ones on Amazon:
https://www.amazon.com/dp/B08QV613ZX -- remove the grips and spray them with a light tan or beige spray paint for a base coat. I used Krylon "sand" colored paint.
-- once the paint is dry, take the lightest colored of the alcohol inks, and put some drops on a paintbrush (a cheap house paint type brush is fine). Wipe the brush over the grips in an up-down direction. Repeat with increasingly darker colored inks, keeping all brush strokes in the same direction. Don't try to cover completely, you want some of all the colors to show through.
-- give the alcohol a little time to dry, then spray on a couple of coats of clear Krylon Kamar varnish.
That's it! The photo below shows the finished result. Compare with these real wood grips on Amazon:
https://www.amazon.com/warreplica-German-Luger-Pistol-Wooden/dp/B00NHNLJRU View attachment 421756