Believe it should be possible to transfer products to sub contractor using replenishment rules
1. You might need to differentiate each vendor by creating specific location for each vendor.
Physical Location/Subcontracting Location/Vendor1 .. vendor2 etc
2. Associate location to specific vendor Contacts > Sales & Purchase Tab > Inventory section
3. On the route 'Resupply Contractor' ensure it is available to be applied on products. Inventory > Configuration > Routes
4. Create replenishment rule for the products (component) - Inventory > Operations > Replenishment
- Min, Max, multiples, location (subcontract location per vendor), route (resupply subcontractor) (Do ensure this route is selected on the product), Trigger (Auto)
The expected behaviour is that when product falls below min qty at a specific subcontract location, replenishment would create a "Resupply Subcontractor" operation. When a subcontract MO is sent to this vendor resupply would not trigger as product is available at this location.
To track material at each location .. Inventory > Reporting > Locations
Filter subcontracting location and group by location
Haven't tested this end to end myself, so would recommend testing before using this concept. An imminent gap on the resupply operation, while the operation is created automatically from replenishment rules the delivery address might need to be updated manually.