Are there figures of people putting up billboards or anything that looks like it can be used for that?

K-line by Lionel did operating billboards like this:

The corner is pealed back and the roller moves up and down, as if the guy is still putting up the billboard. They did a neat Ford T-bird billboard like this. These are around $50.

ARTTISTA makes a figure with a big long brush. The brush is a separate piece. You can swap out the brush with a scratch built roller. It is figure #1214.