FWIW the sled goes on the table saw. I didn't install the runners yet. The stop allows you to cut to the length at the inside of the rabbet so all you need to know is the size of the artwork to accurately cut the molding.
I expect you can buy a steam box although most people who steam bend wood would probably make their own.
Dave's undoubtedly correct that (most) pros build their own steam-bending set-up, but Rockler does sell this kit (along with plans for the box itself) for hobbyists:
Apparently it's not that flimsy. The originals have lasted more than 70 years. The seat slats are 1-1/8 in thick and have a 1 x 1-1/2 stretcher running the length underneath.