Welcome to the forum.
The PAT2 tester is now rather old and it may be difficult to get spares for it, but there do seem to be quite a few PAT2 on ebay and the like and it may be possible to get an entire replacement unit for less than the cost of a new probe.
However I am not sure what test probe you are missing as a flash test is one that is undertaken for type testing of a piece of equipment under initial construction and is very rarely used to test existing equipment and certainly not in a PAT environment.
Class II insulation tests are undertaken using line and neutral joined together and using a probe at points of potential weakness of the insulation or points where conductive material may accumulate.