If you join the Hobie Class Association of North America (HCANA) through this site, you'll get the HOTLINE which is a great publication, with current events, history, repair tips and more.
http://www.hca-na.org/
You can also look at it on-line via the menu at the top of the page.
If you join US Sailing through the "Golden Anchor" program for multi-hulls, you can get "Multi-Hull" magazine, but it is geared more toward bigger boats.
If you go to CatSailor.com, you can sign up for "Catamaran Sailor" magazine, published by Rick White & Mary Wells. It has a lot of good info in it, but most of it comes from the web site.
I'm sure there are others, but those are the ones I get.