I’ve had excellent experiences with Gorilla and Underwood ammunition and wonder whether there are other “small” ammunition makers that anyone recommends trying.

Black Hiils is very good.

I stocked up on Oath Ammo lead-free .45acp a while back and have found it to be accurate and consistent. 115gr copper projectiles loaded into Starline brass. It's been a lifesaver for me here in California where even your sidearm has to contain lead-free ammo while hunting anywhere in the state for any game. I'm not sure if they are still in business but if you can find it, it's good stuff.
Unfortunately, most small ammo makers can only be found online, and that's a no-no in the Golden State.
-Crow