This is really a subset of operations
Remember for procurement/supply chain, first you need to ask objective. In general this will either be "Reducing Costs" or "Fixing/Optimizing Production"
Within Reducing Costs, this could be contract renegotiation, finding new supplies, locking in futures contracts, automating processes (replace labor), changing transport methods, etc.
Within Optimizing Production, this could be a lot of the same i.e. automating processes, finding new suppliers, changing transport methods
Generally, you'll want to segment the supply chain/procurement process to identify problems (i.e. where taking the longest or costing the most).
For Practice Cases Try The Following
1) Search on Operations here (already done): https://www.preplounge.com/en/management-consulting-cases?language=en&topic=8&sort=real-case-desc&page=1&perPage=20
2) Google and casebooks are your friend. For example (https://managementconsulted.com/case-interview/case-interview-examples-master-list/)...go to Accenture, Amex, AT Kearney, Deloitte, and LEK sections which specifically call out operations.
3) Send me a message and I can provide you with a few good ones and/or case you in them!