For devices with proprietary MIB's or Enterprise MIBS, you should obtain them from the vendor, Google is very helpful and add them to your MIB's in ~/mibs, before doing the SNMP walk.
For a large collection of MIB files which have been error corrected, you can find many MIBS on Keith Sinclair's GitHub MIB Repo
Commands to run:
mkdir ~/mibs cp <vendor mib file(s)> ~/mibs cp /usr/local/nmis8/mibs/traps/* ~/mibs snmpwalk -m ALL -M ~/mibs -v 2c -c GOODCOMMUNITY <HOSTNAME or IP ADDRESS> system
Run a full walk and redirect to a file, note that you can use snmpbulkwalk on many devices when using SNMPv2C, this greatly improves the speed of collection on very large devices.
snmpwalk -m ALL -M ~/mibs -v 2c -c GOODCOMMUNITY <HOSTNAME or IP ADDRESS> .1 > ~/VENDOR-Product.mib or snmpbulkwalk -m ALL -M ~/mibs -v 2c -c GOODCOMMUNITY <HOSTNAME or IP ADDRESS> .1 > ~/VENDOR-Product.mib
Now you have an SNMP Dump.
This page has great information about Modelling MIBS that use Indexes using the systemHealth section.