Can anybody suggest a good tool for Spare Management?

If you are referring to an IT solution for stock control and inventory management then that's depends on volumes and emphasis.

an ERP if tuned to the demand of a highly skilled inventory specialist would be great but I'm yet to see a perfect one. 

If you are using a warehousing system and have a bigger emphasis on warehousing than sales then definitely SAP.

for your average importer/dealer however I'd stick to ADP/Autoline/Kerridge