Whole books have been written about this topic.
Yes, better deals aren't found on the MLS, especially in seller's markets (as most are nowadays.. a few years ago this may not have been the case).
There are many ways.
A few include:
MLS
Networking (with agents, for pocket listings, with investors and wholesales).
Direct marketing (bandit signs, yellow letter and postcards, driving for dollars, probate, out of state, etc. etc.)
Websites (craigslist, auction.com, various fsbo, etc.)
There is no shortcut. The latter few aren't magical codes and are less likely to have deals. The lower the barrier to entry, the more competition there is.