MIB files can be downloaded directly from the Gateway Console.
See: Legacy SNMP for Ethernet Gateways for more instructions on downloading MIBs
There are two MIB files. The standard EG4 file is for use in standard SNMP applications. The VIP MIB file is used when using Virtual IP addresses for each monitoring node instead of the standard 16 digit GUID embedded in the OID.
If the link is not available on the console this may require that the Gateway firmware be upgraded.