I'm only guessing here, but I bet the same caps are used on most 41mm forks of this style. Yamaha doesn't make the forks, they outsource them, as do most of the Japanese manufacturers. I'd look at a wrecking yard that specializes in motorcycles, tell them what you have, and I bet they will come up with what your looking for. You can find yards that sell motorcycle parts online. Google is your friend.