A "craigslist" post and a notice board flyer at the feed store will generate more leads than you can deal with.
The hardest part is turning down an eager owner whose property is unsuitable. You feel like you want to make them happy, but just have to say no.
Just like in retail or real estate: location, location and location.
Unless you are going to be migratory, look for season long forage-- diversity, woodlots, hillslopes, creeks.
(for my yards> Arroyo Willow>Eucalyptus>White Sage>Wild Mustard>Toyon>Buckwheat>Coyote Bush takes me from December to October without a nectar break.))
You want to have access that doesn't involve making an appointment. I've tried yards where I have to call a day ahead, and it just doesn't work.
An owner with an interest in the bees and regular observation really helps -- if the bees swarm, or the hive goes wonky or a tree falls over -- its nice to have a pair of eyes.
It a great way to meet new friends. Its definitely a relationship that must be cultivated and developed, and because you are meeting over sweets and fruit of the land it can be really positive.
Everyone should have an out-yard, because manipulations are so much easier when you can change locations, etc.
The reasons yards don't work out are innumerable. I set up in an Apple-Mandarine Orange-Avocado Orchard and thought I was golden, but the next spring the farmer said I had to move because, "the trees set too darn much fruit, and I spent my whole summer thinning". Cannot win for losing.