The Theatre Historical Soc. often learns of fixtures for sale, and you can phone them, or simply place an ad in their Newsletter. See the link by that name on their sidebar:
www.HistoricTheatres.org
In regard to getting any fixtures, remember that quality is best in the long run. As you surmise, not every fixture is built for the use that you will put it to, so look for a fixture with porcelain sockets, or at least an open top fixture that allows for lots of air movement and easy relamping. Many art deco designs would fit this description. If you will be using compact fluorescents exclusively in the fixtures, be sure that the intended lamp will fit the available space without touching anything but the socket, and that there is enough room for it inside the fixture (many fixtures were designed for a specific type of incandescent bulb -- usually the 'A' type -- and compact fluorescents are often too big.) Don't take a salesman's assurance; insist on taking a fixture in hand and putting in your intended bulb to make sure it fits. Porcelain sockets are most needed for higher wattage incandescent bulbs, but they are better quality and would be nice for fluorescents as well, as regards longevity. Also consider multi-circuit fixtures if your locality requires automatic emergency lighting, as many municipalities do. These might be incandescent sockets even of plastic, since they won't normally be in use, and will operate on low voltage battery supply, which most compact fluorescents won't. This would eliminate having to use those ugly flood-light battery units sold everywhere, if you are in a position to run low voltage wiring from a central battery/control in a back area, where the battery would be a lot more accessable!
I probably don't have to mention this, but you want your fixtures out of the easy reach of tall fellows who are on the basket ball team, and might think it 'cool' to reach up and take a bulb or even a part out of a fixture. Moral: all fixtures should be accessable only by ladder, else must be closed fixtures not too easy to open. You would be surprised at how inventive vandals can be! For the same reason, the fixture should accept some heavy wall bolts (yes, more than one) to anchor them securely, lest you find that the 'patrons' consider them neat souvenirs. Of course, if you really like the design, you will want to keep at least one extra fixture in storage, if not more, for the inevitable breakage from relamping or whatever that will take place over the years. Best Wishes, Jim (member [url=http://www.HistoricTheatres.org)]www.HistoricTheatres.org)[/url]