Sorry you missed out on that .45 Camp Carbine, but as Marlin made a lot of them, I think you'll find another one! The only reason I don't have a .45 Camp is because I already have a very nice Mark 45 Carbine (semi-auto M1 Thompson lookalike). Shop for a Camp Carbine in very good to excellent condition, only! I've seen a few that were not treated well, but the owners of the .45 versions seem to be more respectfull of theirs than the 9mm owners. Just a trend I've noticed.
Weemsf is correct that there are velocity gains to be had from handloading for one. +P loadings with fast powder often yield an additional 250 to 300 fps over a standard 5 inch pistol barrel. +P loads with slower burning powders such as HS6/W540 or Blue Dot often yield an additional 400 fps over a 5 inch barrel. Some times more. The Marlin Barrel may be even tighter than that of my Mark 45 Carbine and yield even higher velocities. Hope you find a Nice One!