You can custom order 88mm pistons from JE Pistons to the spec you want if the Kameari options don’t do it for you.
As for bore and issues such as core shift, wall thickness, etc., there is a serious lack of imagination on the web, mainly stemming from the fact that most of the English language discussion of the topic is US-derived. E.g., just because there seems to be a lack of choice in the States with respect to engine shops capable of doing metric block sleeving (or it’s considered too expensive) doesn’t mean we have the same problem.
89mm and up isn’t an issue when the cylinder bore is brand new with a known wall thickness...