I signed on as a full time employee for the facility that I had been going to through my registry, but managed to get enough 40+ hr weeks in the 18 months prior that I was able to stick with just one registry. For the first 6 months or so it was patchy though. I didn't always get as many hours as I wanted, although I did make enough money to pay the basic bills.
I found that in AZ, even if you are working for a registry that is used frequently for your specialty, you have to work in each place enough that the people who call the registries know your name. There are dozens of registry nurses, so when you are not well known the best thing you can do is accept as many shifts as you can work at a variety of settings, and then if they need someone for a double shift, stay. Let the facility know that you are available for the next night if you are. You can't book your own hours, but continuity of care and convenience actually matter, and they will try to get the same person as much as they can. If you are at a large facility, and you let them know that you are looking for more shifts, they will usually oblige.