Hello JGB: There all over the place on the net.
See:
Ham Radio Amplifiers | eBay
Back in the early 80's I bought a 1973 Duster for temporary transportation from a good friend, he said it needed a new battery and fresh gas. And a 100 bucks I am on the road. It had a small 150 watt or so amp installed in the truck with that black undercoat spray all over it, hiding it, I never paid any attention to it. The Duster had a M125 antenna mounted to the trunk lid, and man did that little amp and antenna get out. A few years later when I sold the car I realized what the black box was mounted in the trunk. Wow that little amp really worked good. On the way to work in the mornings I had all kinds of skip stations calling me to wave a hand.
So all you need is a small amount of power increase. A 100 to 200 watt amp will work well for starters.
It will need to be wired directly to battery using 8 gauge wire or better. Most antennas will take that much power.
Most guys just want a little more power to get out, just a few are the "mine is bigger that yours" types.
Good luck.
Jay in the Great Mojave Desert