When we were on Magento 1, we used a Crius Dropshipping module (no longer around) which created a purchase order with the customer info for each vendor who had a product in the order. The POs were generated at the same time as the order confirmation and they were sent to a designated email address for each vendor (I had them sent to me and I forwarded them to the vendor).
The module utilized transactional email templates that I set up for each vendor. It was pretty basic, but the email PO is all I really needed since I don't manage inventory.
It seems like this would be a fairly easy feature to add from a development standpoint since it mimics much of the order confirmation functionality.