Hi Chefiam1, sound like you have a bit of a jigsaw puzzle to assemble. If the mechanic who disassembled it was any good he would have punched some witness marks into the cylinders and the crankcase. Look for center punch marks, a single on one and two on the other. He should have done the same with the cylinder heads, if not do not panic. The cylinders and pistons are likely to be identical and interchangeable. While it is always better to fit them back in their original positions honing the cylinders and fitting new piston rings should sort out the problem.
The first thing you need to do is get yourself a copy of the service manual, these are available from a lot of online stores depending on what country you live in. Despite what the mechanic told you spares are available, you just need to know where to look, this also depends on which country/continent you live in.
Bob