>Is it common for broadway casts to make it into "mainstream" magazines?<
Yes. Vogue and Elle write about new and notable Broadway and Off-Broadway theatre productions pretty much every month, and Vanity Fair selectively spotlights new Broadway productions. Just this fall, for example, Vanity Fair featured photos of cast members from Chorus Line, and Bill Nighy (The Vertical Hour) is on the cover of this month's Fanfair section in Vanity Fair. Recent Vogue photos and articles included Kristin Chenoweth for The Apple Tree, Ashley Brown and Gavin Lee for Mary Poppins for Vogue and Raul Esparza and several of his other Company castmates.
Other national magazines like Time and Newsweek also write about the theatre on occasion, although not to the degree they once did. Entertainment Weekly also has a theatre column about once a month, and does a theatre story or spotlight article every now and then.
Begin at the beginning and go on till you come to the end: then stop.