When I retired as a carpenter I got a job with Wood Workers Warehouse that is now defunct. We sold Reliant tools . The shaper was one of the tools that never got complaints. I am not sure if Jet, Grizzly or other importers would have what you want. Try talking to a tech and include as much information as possible. Include dimensions if you can.I don't intend to use very small cutters. It's just that I have some of the form cutters I have are with 1/4" shanks. I've had good result with 1-1/4 dia cutters.
As far as the 1-1/4" arbor, I don't intend to use particularly large cutters either. I have one or two that are around 4" dia with 1" hole.
If I don't go over that, a 1-1/4" hole wouldn't cause any issues.
I suppose I could use a straight collet reducer to go from 1/2" to 3/8 or 1/4"
Also there is a forum for older tools, I do not recall the name.
Also try Accura , I believe they have the same parts as Reliant did