Plain old cold-rolled steel bar stock will work to make that adapter. Start with a piece of 1" diameter stock so there will be a flange to support the bearing race from the back side. If you want to get fancy, use air-hardening drill rod to make the adapter, heat it cherry red with a torch, and let it air cool. It will end up being as hard as woodpecker lips. I'd choose not to do that, or at least not to harden it if you choose to use a tougher alloy than cold-rolled. You'll need a .750" ID shaft collar inboard of the bearing area to keep the adapter in place.
Drop me a PM if you don't find a machinist locally.
Jerry
