There's a part number for every piece used on a pinball machine - sometimes the trick is to find it.

The entire assembly is an A-16654 "Opto Plate Assembly". If you look at page 2-43 in the manual you'll see callout number 17 points at the front of the captive ball assembly; look that up on page 2-42 and you'll find the part number for the assembly.

The game-specific piece on the assembly is the 01-11469 metal plate. I cannot find any vendors that sell the assembly or the plate. The plate would be fairly easy for a machine shop to fabricate if you had a pattern of the original to work with.

The captive ball wireform ramp is 12-7076

I think it may be A-16654 Opto Plate Assembly. Is it what the captive ball opto attach to?

Somebody beat me to the punch (with a better reply too)