I have just handed over my car and converted ZVH block to get the work carried out, but when mentioning the 2.5 - 3mm spacer needed behind the pulley, he looked at me a little confused. I know nothing, hence why asking you lot here..

Taken from Quantums page:
A 2.5 or 3mm spacer is needed behind the camshaft pulley to equalise the distances of the pulleys from the block so the cambelt runs fairly close to the centre of all the pulleys.

Is there are quick remedy to this, as in a shop bought spacer, or what else can be used?

I can't open the quantum spreadsheet as i havent got Exel on this computer.