Belt Mountain had their “Punch” bullets that were solid brass. I believe the were milled and not cast. I still have a box of their 45-70 and .357 mag from Grizzly Ammunition. It is very gnarly stuff.
I'm thinking there are a couple of bullet manufacturers that do, or have made solid brass bullets at one time or another.
I Googled "brass bullets" just to see what popped up.
The Solid Bullet (SD) - Nosler Solids™ feature a flat-nose design and homogeneous, lead-free alloy core that reduces deflection off of bone and muscle, for lethal penetration and an impressively straight wound channel.