How do you source meat that will be minimally cooked?

The thing to remember, vis a vis bacterial contamination, is that it's almost always the OUTSIDE of the meat that's contaminated, not the inside. With pork and chicken you're worried about an internal parasite/bacteria, which is why they're not cooked rare.

With beef, if it's grade A, it's good to go, and most everything you buy in the grocery store is fine. With tuna (which is another one people like super-rare) the story is mostly the same, though the chance of getting a parasite from fish is higher. In both cases, do a hot sear on the outside, and it'll take care of any bacteria that may be hanging around.

The reason ground beef is considered a higher threat is because the "outside" is pretty much the whole thing after the grinding process.

If you're in an area with a large enough Ethiopian population, ask around where they shop. There's are Ethiopian dishes such as kitfo and gored gored that feature raw beef, and they take the preparation very seriously. If you have a specifically ethiopian butcher in your area, it's a good bet.

Other than that, I'd go with a busy butcher -- the busier they are, not only is it a sign that people aren't getting food poisioning there, but they're also turning their product over faster, so it's likely to be fresher.

You might also see if there are any places that will sell you a whole primal in a cryovac packaging (even some grocery stores will)-- this would mean that it was sealed at the slaughterhouse, and I would hope it's had less chance for contamination.

You could cook most beef blue and black -- what that means is seared on the outside and pretty much raw on the inside. These days it's seen most often on Tuna -- seared on the outside and still cool on the inside. I think that's what Satanicpuppy was talking about.

Find a butcher who knows what they are talking about, can tell you where the meat comes from, and most importantly cares about the meat they sell. Ideally, they buy direct from local farms and can tell you where everything came from.

The biggest problems from supermarket ground beef is that they combine meat bits many different farms, allowing one bad cow to ruin the bunch. Grinding your own beef or finding a place that grinds their own on site is the safest way to enjoy a burger at anything less than well done.

In Finland I've eaten reindeer rare, even made tartar out of it - totally raw. I didn't even need tenderloin for it, even haunch was tender enough, actually I liked it better then the more expensive tenderloin.