I have created my own horn button for my project, and in the process, decided to make a few extras for sale and to recover the investment.
There are two sizes, the MOMO Style, that fits 6 screw steering wheels, and the larger for 9 bolt steering wheels. I can sell you the complete kit with 15” steering wheel and adapter or just the button.
I currently have 5 of each size
San Diego, Ca
Momo style button $50 (with screws and wiring).
larger 9 bolt button $150 (with screws and wiring)
steering wheels are $170 and adapters $75