Years ago, Group Publishing actually had an entire magazine devoted specifially to junior high magazine. They discontinued it a dozen or so years ago but have decided to give it another try...almost.
Instead of a magazine, Group and Simplyjuniorhigh now have a monthly 12-page newsletter focusing on junior high ministry. Each issue will have some training, some research, some interviews, some lesson ideas and some other really great stuff. Forty Bucks for a year feels a little pricey, but it's probably the cheapest way to get ongoing, monthly training and encouragement.
I would suggest you buy one subscription and then photocopy key articles etc. to give to the volunteers on your team (but I don't know if that's legal!).