For MMI, if you buy the The Marine Modelling Plans and Construction Guide , there is the MMI back-issue content and availability listing included.
As for Model Boats, I'm not sure Nexus/Highbury ever published such a list. In fact, come to think of it, did they actually sell back issues?
You can try visiting Magazine Exchange, as they sell back issues of Model Boats magazine, and list for each issue a brief contents.
http://www.payhost.net/magazineexchange/acatalog/Model_Boats.htmlMITS
