I don't get what the problem is here. The pot has done 7 years. It's knackered. Ho hum. Yammy will supply a direct replacement that will do probably another 7 years for just $25 shipped. That's less than 7c a week. I appreciate that the piano cost $5k (Aus ??) initially, but at the end of the day, it's not exactly a Steinway, is it ? You could pay that much for a top end LCD TV or a mediocre plasma, and find that you couldn't get parts, or that they were prohibitively expensive, as little as 2 years down the line.
You might even have just been unlucky to have your pot fail in 7 years. If Yammy don't have it available anywhere in your country, needing to de-stock it from Japan, that might suggest that there is little call for replacements.
Personally, I wouldn't give myself the grief of trying to shoehorn an alternative in, with no guarantee that it's going to perform as the original did, when a direct manufacturer's replacement is available at what I think is a very reasonable cost, and with a life expectancy of at least another 7 years. Half of that cost is probably shipping and handling anyway, so get two whilst you're at it for probably not a lot more, then you'll be ready to roll again in another seven years ... d;~}
Arfa