MIB for my NIC cards

Hello; I'm trying to get regular polling of the errors, txqueue
length, and dropped packets from my ethernet cards on a machine. I've
already got snmpd set up on it serving other data just fine; it's just
that I can't seem to locate the MIB for these particular devices (and
associated subtree that would have these errors accessible) anywhere.
I've currently been trying to locate them by hardware vendor, I guess
that might not be the right path to be taking... Perhaps I should be
looking in subtrees of the associated device? (ie eth0, eth1)

If anybody knows where I might be able to look for this information I
would definitely appreciate it. :)

Oh not sure if this matters but the hardware device is a RealTek
RTL8139.

Thanks!

-Damon
.