Complicated process for replacing items on inventory

Looking to see if anyone has a similar issue and how they have resolved it.

We sell scanners to resellers who then send those on to customers. Those customers might then to replace the scanner while it is on warranty. We cannot create a RMA on it since we dont know the original purchase and we dont have that customer in our system. Also - this is a replacement and not a refund for credit (those go directly through the reseller).

What is difficult is getting a process that traps all the information we want on the return since again we havent sold anything directly with them (or we could just do a $0 RMA and a $0 sales order to send the replacement unit back to them. As well, since we would like to do this through the customer service role, these users have no access to RMAs or Sales Orders in the first place.