Where do you look for rare records and pressings ?

There are some trusted dealers out there, but no assurance that they have what I am chasing at the moment and prices tend to be higher than what I can find on the usual sources like E-Bay (country of origin in some cases) or Discogs. Every once in a while a general web search will yield gold. I found a dealer that had bought out Lloyd McNeill's old stock of records- the early ones were on a private label and the masters don't exist any more. Finding those in the wild was close to impossible. Sometimes you just get lucky. 
That WFMU show in NYC is about as good as it gets in the US as far as I'm concerned. Haven't been to Utrecht though. 
I also have a friend who is a serious buyer of records- he has his own labels and is a distributor, but spends his free time chasing records. He finds all kinds of stuff and will include me in his buys-- winds up turning me on to a lot of stuff I never heard before. One of his favorite sellers had a table at the FMU show that I culled through a couple years ago. I did not recognize ONE record! Obscure japanese fusion/jazz. Some of it isn't necessarily my cuppa, but it is always interesting to push the boundaries. 
Believe it or not, I've gotten rare records from Amazon sellers! :)

Discogs, unless (once in a while) my local record shops have what I'm looking for, and I try to support the local guys whenever possible.

Most of us that have collections built over decades have some simple rules, like buy it where you can... and never pass up the one you want, as you may never see it again.
There is no easy to flip switch that makes for ease in getting to a bigger collection. If there was, we'd have all marched through that door ourselves.

You gotta work at it. For a long time. No shortcuts except that of money.

Yeah, chase never ends. Since I don't need many records I have an advantage when it comes to the price, within reason. Couple of records a year is fine. Trusted dealers is a good idea, those that kind of accept special orders.
By the way, I ignore amazon as much as I can, it is a monster company closely aligned with the government, not the best part of the government. I don't care what they got.

Yard sales pretty much dried up around here in N. Va twenty years ago, after a rapid decent. And it used to be so great for a long time, maybe the best in the country. I could hit fifty yard sales a day on a good day. Maybe it’s all the recessions, but now it’s only dirty baby diapers. eBay is the final frontier.