The first six characters in a MAC address are unique to particular network equipment vendors.
This web site shows the identifiers for Xerox:
https://www.adminsub.net/mac-address-finder/xerox
This site shows that there are sixteen unique strings that are associated with Xerox.
You can start typing in these partial mac addresses one at a time in the search feature on the Meraki dashboard
(hit the / key to open the search bar) and see what devices show up.
This is not ideal and could take some time, but it should show you most of the Xerox devices on your networks.