Big-Bore Piston Help

I have a 1998 KTM 250 EXC dirt bike. I had the bottom end rebuilt and the cylinder replated. They replated it to 68.50mm. Stock is 67.50mm bore. Now I am having issues with finding a piston that fits. I am looking at a Wossner piston +1.00mm 68.44mm for a big bore. Most options are in the UK and over $300.

I am new(ish) to dirt bikes but mechanically inclined. Do any of you have some insight or tips on where I can find a piston that fits my bike?

Thanks in advance.