How do you hunt?

[bw4sale]

I'm new to piecing together a project and have never done any junkyard hunting or anything. When you are looking for something specific like a certain model trans, what do you do? Do you call the junkyards around or do you have to go look? Will they be able to tell you if they have that specific part or will the just tell you if they have a vehicle it might have come in? Do you post an add on craigslist or anywhere? 70BLAZERX2 showed me Car-part.com. Are there other resources like this? I'm looking for either an NV3500 or an AX15 5-speed for my project. Thanks.