In general you just buy a tiller than matches the profile, or adjust it to your needs and go with it. If you want it matched exactly you will likely have to send your old one to someone to replicate. When I bought one for my old Lancer 25 I purposefully bought it a couple of inches longer so I could keep the tiller in one hand but comfortably reach the main sheet on the cabin top with the other.
Call H&L Marine.
H & L Marine Woodwork, Inc.
2965 E. Harcourt
Rancho Dominguez, CA 90221
Tel: (323) 636-1718
Fax: (323) 636-1720
They supply West MArine, APS and many other marine suppliers with tillers. You can buy from them direct or through a reseller. There's another company that makes them in Idaho, or Utah that I've seen ads for. I'll post a link if I see it in the next week or two. But H&L is the most well known.
Measure the length, the butt dimensions and pick the style you want. You may have to shave a little off if its too big, but it's pretty straighforward. You will have to drill a few holes to bolt it to the tillerhead, But be sure to revarnish any freshcut wood. Mositure can get in there and cause rot.
Good luck.