Gas cap for a 1984 FJ1100

[AndyBCcoast]

Hello, I am new to the forum and new to FJ ownership.  I have a 1984 and a 1985 FJ1100 that I recently bought and am starting the process of recommissioning both bikes.  I realize that this is going to be a marathon and not a sprint, so the intention is to get at least one of the bikes up and running for the Spring.  Both bikes are complete and in good cosmetic condition.  The 1985 is very low miles, 10,000 km, although I am not convinced that this is genuine.  The 1984 has 77,000km on it and was owned by the same guy for 30 years. 

I am looking for a gas cap for the 1984 bike.  My reading around the topic has shown that these are difficult to find but I am really hoping someone out there will have a cap they are willing to part with and help me out.   

The photo of the tank shows the mount type I am looking for, the second photo shows the type of cap I believe I am looking for.

I am probably not the first person to be looking for a gas cap such as this, if anyone has found a substitute or a workaround, please get in touch and let me know what your solution was.  Thank you in anticipation!

All the best

Andy