Where do you look for rare records and pressings ?

Personally I find what I need on Discogs. But you may be looking for a trusted dealer with a carefully curated stock, perhaps somewhere like Brooks Berdan which keeps a selection of audiophile approved records - you will pay top $ however

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.