Add a quote for a special product and link to a purchase order
When creating a quote you can sell from stock, catalogue or special products. Special products are non-stock controlled and have no default price. They do have a stock method appropriate to how they will be purchased and sold, and have no default price or cost.
Specials should be used to one off items that are not going to be stocked and are unlikely to be sold regularly.
With a special item it will either be created out of other stock items (using Mill & Return lines) or purchased from a supplier, either on a back-to-back or direct purchase.
This video gives a brief example of raising a quote for a special item and generating the purchase order to get it in for the customer.