I don't know of a print magazine dedicated to Lightroom.
Check out Matt Kloskowski's Lightroom Killer Tips website with info tutorials & videos:
http://lightroomkillertips.com/
They also have a Podcast on iTunes and a video feed at
http://kelbytv.com/lightroomkillertips/
Layers Magazine is an online readable magazine dedicated to Adobe products & features Lightroom plus the other Adobe packages:
http://layersmagazine.com/