Plastics properties in general vary considerably. The conductivity will vary depends on the drying process of the paint. If you need only an approximation, the manufacture would give you a range. For specific value you will have to test it yourself. I have found that if the paint was applied in humid day the conductivity is very different then if it was applied on a dry day. (almost an order of magnitude)
howkers-
Why are you looking for this? In the vast majority of problems, the thickness of the paint layer is so small that the paint has practically no effect on conduction.
Tunalover