The source list is material related, it has no field for material group. Just look at table EORD.
A source list is anyhow just a filter to the sources. A source is an info record or a contract.
It is also unclear what kind of planning you want do which shall automatically determine a source. MRP can do that via source list, but MRP runs for materials, not for material groups.
An info record at material group level is considered if you have no material number in your requisition.