About 1 out of 3 startups from our last fund were not YC. Many came from warm intros, but a few I scouted and found myself. I went out and recruited Bannerman to YC personally (they're focused on security, which fulfills a key role on Maslow's hierarchy of needs), for instance, and then later invested afterwards.

Cold inbound emails haven't worked well for me, but that's where software down the road should help.