Having never owned an Italian gun, I don't know what the comb hardware looks like but machined aluminum or steel spacers can be had in the form of AN washers used on aircraft and race cars. The come in bore diameters from 1/4" to 3/4" and thicknesses of 1/64", 1/32" and 1/16". They're used in stacks to align nuts with bolts for cotter pins. They're very accurate and not ugly like hardware store washers. Link above.
You can't buy the Perazzi kinds at the hardware store.
They come in 1mm, 2mm, 4mm, and 8mm (double sets).
You can combine the 1+2 to get 3, and obviously you can combine them all in such a way to get all the millimeters from 1mm to 15mm. I not sure you can get that close with washers, or even if it's important to get that close.
I've sold two set for $40 each - all new sets.
Hardware store washers would be cheaper, of course, but the small diameter of the Perazzi ones permit you to check the cast marks should that be necessary??
If you know what you need I'd be happy to run off a couple at the states heights to fit the Perazzi risers for you.