Does anyone know where I can find some MIBs for an Watchguard Egde X20e firewall?
Have you tried to contact the vendor/manufacturer? they should be able to provide you all the mibs created for this device.
Also if it's possible to change the name from net-snmp to Watchguard?
Check that thread => Re: Juniper SA2500 MIB Support
which is linked with => Re: NET-SNMP?