Had a similar problem with a Kohler K181 engine after inspection when I took it apart. Got a rebuild kit from the USA with an oversize piston and struggled to find an engine reconditioner that would do the rebore. They had the machines set up for large engine blocks and one said just breaking it down and setting it up for a small block would take the best part of an hour. But did eventually find a chap at Kidderminster who does them. You may have to make many phone calls, but will find someone somewhere. A tip maybe is look to see if they do British motorcycles, there are several in the West Midlands. The Kohler rebuild kit only cost about £70 and was a bit sceptical if the parts were of reasonable quality. Should not have feared, they were fine, with ideal limits and fits tolerances. Have a mate with a Honda GX160 on a Merry Tiller that smokes like a steam engine and runs terrible. Am going to take that apart this winter and if the bore is within service limits, will get an after market rebuild kit for that too. Can you believe they are less than £20.