Painting the buttons would be a bad idea I reckon as

1. It would slightly alter the shape / fit
2. The paint would wear off

I found this too ...

Now, once the powder is mixed with inks and painted or silk screen printed, the lifespan is over 5 years if used indoors and 1 to 2 years in an out door environment. Plastic molded products have a longer life span of over 10 years.

You have to order 5kg which will cost about 115$, but they can get sample batches.

Does anyone have the right experience / facilties to make up the buttons from this material.

As mentioned, no soldering, and personally I think they would look OK.