Splitting purchases between vendors for 1 product - How do I use D365 to have 2 vendors where every other PO is placed with a different vendor

We have very high volume raw materials and we need to maintain dual sourcing by order from both vendors at a consistent frequency.   The system only allows to set up 1 vendor per item (although others can be approved).  I need the buyer to get the message to alternate orders between the 2 vendors.