Can't say much about salvaged cars, but I've been through several searches for manuals in California, nad can tell you what I've learned, read and been told.
Back in the good 'ol days (cue sepia-toned flashback scene) - say, 20+ years ago, automatic transmissions cost several thousand$ more than manual transmissions, and they got much worse fuel economy. Now fastforward to the 21st century, and while it's true manual transmissions still cost a bit more and get slightly worse fuel economy, those two gaps have narrowed considerably.
When researching cars sold in the US (and particularly in California), I was amazed at how many car models simply do not offer their manual transmission version in California. For many models, you simply cannot get a new car with manual transmission at any dealership, even though the same car might offer a manual transmission overseas or in central/south America. This of course means there aren't as many mustachian manual-transmission used cars out there on craigslist.org
This bugged the crap out of me, so I asked lots of different people this question, from my mechanic to car dealership sale's reps to a few motorheads of mine. The explanations they collectively gave boiled down into the following reasons
1) Fuel prices in the US are comparatively cheap, so the 'savings' from driving a manual transmission has been a non-issue for most. Americans have been notoriously slow to care about MPG ratings at all.
2) The gap between the extra cost for an automatic and the difference in fuel economy has narrowed so much that it's a non-issue, particularly since most new cars are financed, and we are really bad at understanding that an extra $22/month (for the automatic, fancy-car edition) on a 5 year car loan is actually a really big deal.
3) In the US (and especially in California) the expectations for what's included in a car are higher than anywhere else. Here we expect to have a/c, power windows, a decent radio we can plug our iPod into, etc in our base models. In other markets these cars would be the luxury editions. The no-frills trim line found in other countries simply aren't sold here in the US. This has extended to manual transmission cars
4) Since manual cars are relatively rare here, it's set up a feed-back loop, where teenagers never learn to drive a manual because daddy/mommy didn't own one, so they will only buy an automatic when they make their first car purchase.
First world problems, eh?
I'd just like to point out the reasons listed above are for the people the marketers really care about - the non-mustachian clown consumers.