So this fell in my lap, I need to write an SNMP MIB for an in house application, essentially just to let a customer receive traps(in practice I think it'll just be one trap, at least to begin with) ...

SILVER SPRING, Md. – The Security Industry Association Standards Committee has announced plans to begin work on a security industry-specific set of attributes relating to Simple Network Management ...

They are usually vendor specific and therefore available at the vendor site, unless you are talking about the generic standard interface counters. I doubt there are any custom counters on a cheap ...