What exactly are you guys doing that's making rares so hard to find? Are you doing only SK runs? Here's what I do and my experience:
1. I only do SK runs to go from lvl 11 to 13. Not because I want to, but because Blizzard forces me to do that if I want to join public games. I have found only 1 rare during my 50+ times of doing the run over 6 characters.
2. I always start new characters as soon as I reach lvl 13 on my current one. I have found all my rares by walking around in the open areas and crypts that have little to do with the main storyline.
3. I explore a lot and usually find every single champion. Champions drop a lot of rares. Bosses are the opposite. I turn over every corps, blast every urn, and check everything that can be clicked on. I think around 5 of my rares came from one of those.
So yeah, if you are not finding rares by doing SK runs, perhaps explore more? I don't know. This is just my experience. Hope it helps.