this may sound a bizarre question but I need to track a car based solely on its tax disc number (long story short but all other info given me was false)
If the other information relating to the vehicle was false (reg. no., insurance, owner & driver details?) what leads you to believe the tax-disc information is genuine?
I know each tax-disc has a unique reference number, so maybe the Shannon, Co. Clare contact for vehicle registrations, etc. might be your first port of call.