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often turned up some useful information - though as with all such listings, some of the listed OBCZs (and LFLs) are no longer active.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 It could be based off of the hunting-page release zones that have been tagged as OBCZs, but those are often out of date so some effort would be needed to verify them.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!