Descripotion in here does not mention any spacer.It is not completely clear.
No need to source the spacer, why not using normal washers or other distance pieces and testing it again to ensure you really need them.
But:
If the speed sensor has been removed or replaced due to an ABS fault, a traction control fault, or as part of post-accident repairs, a functional test must be carried out using the Porsche System Tester 2 – via the ‘Actual Values’ menu, ‘Speed’ submenu.
And:
The optimum air gap (the distance between the sensor tip and the ABS ring) in these systems is typically between approximately 0.5 mm and a maximum of 1.5 mm.
Plus what I found:
The aluminium wheel hubs on early 996 models, in particular, are extremely prone to oxidation around the ABS sensor mounting. The corroded aluminium pushes the sensor up slightly (increasing the gap). Garages then tend to scrape the bore clean. If too much material is removed in the process, or if the factory-fitted spacer is omitted, the new sensor will sit too low