If it's a loose hub it's much easier. Sprocket blanks are easy. Most bearing retailers carry them. We make aluminium rear sprockets and as such have a reasonable stock of big ones. Not a lot of use to you.
No point in buying a quality sprocket blank as the welding will change it's temper. If you can't find anyone near to you John I can do it.

email (option): pes.sales@btconnect.com

Mark...Do you know anyone that can produce from a pattern a 46T, 5/8" x 3/8" aluminium sprocket for me?...I've been trying to get one manufactured without success so far for my latest project...Ian

email (option): ian@wright52.plus.com

I have had laser welding done successfully by EMP Tooling in Havant.
Expensive but no heat issues

I should be able to make it. My stocked sprocket blanks are all 5/8" x 1/4"

I've found a sprocket blank 5/8" pitch 46 teeth and 9.1mm thick, so should be easy to do.

email (option): pes.sales@btconnect.com

Mark...You have e mail...Ian

email (option): ian@wright52.plus.com

Hi mark
I’ll call & talk on this one
I’m relocating in the next few days so am a bit stretched & busy with non motorcycle stuff
Br
Job

email (option): jonnyob1@googlemail.com

Brasswelding