Those are great knives! I have the large and the small version. Both built to survive the destruction of mankind. I've used my large one to chop wood, cut heavy fiber rope and pry wooden crates open - none the worse for wear. The small one is still NIB in the safe.

I'm thinking a soaking in paint remover for the blade would likely do the trick. As for the handles, maybe roll them in a rag dampened with paint remover and leave for a day ...then a gentle wipe down with a rag/soft toothbrush.... or contact Buck and see if they have new ones...to include the sheath. Getting all of that paint off the fabric will be tough.

They are great knives, but not "that high" collectability wise, so giving it your best shot won't hurt. Worst case, you'll still have a great field blade with wear.