Don't forget to order your supplies for this year's International BookCrossing Day (April 21)! The last day to order them is March 25, because we'll need time to get them to you before the big day arrives. And this year's labels were designed by Azuki and they're great. So don't miss out, get your orders in while you can!
There isn't a site-official one, but the header of the OBCZ Managers forum ( http://www.bookcrossing.com/---/27 ) includes a link to a Wiki, but while I was able to load that one I didn't see much in the way of listings.
The LibraryThing site does include member-added listings of "little libraries", which can include BookCrossing OBCZs as well as Little Free Libraries. I've done web-searches for "LibraryThing, little libraries, name-of-town-and-state", and have often turned up some useful information - though as with all such listings, some of the listed OBCZs (and LFLs) are no longer active.
It would be nice if this site had a "find nearest OBCZ to me" feature - in fact I'm sure that's been requested in the Features forum in the past - but I don't know how hard it would be to implement. It could be based off of the hunting-page release zones that have been tagged as OBCZs, but those are often out of date so some effort would be needed to verify them. Maybe someday!