How would you recover costs for materials that a subcontractor should have bought but didnt? Would you recover through a compensation event?
You can only recover this from the Subcontractor if indeed it one of the reasons under 60.1 that it is one. I assume from the question this is an option A subcontract.
If the Subcontractor managed to meet the Works Information requirements without providing this material then actually no - this would be their benefit (under option A). If it was an express requirement then this would be a Defect which either has to be corrected or the Contractor can give a quotation for a saving (or you make them provide the materials. If you had instructed them not to provide these materials then this would be assessed as a (negative) compensation event.
Depends a little but therefore on what exactly these materials were and who/how they were to be provided. Once you have looked at this then follow the rules above.