Now there's an idea...the Polish maritime modelling magazine Modelarstwo Okretowe published 1/150 plans of each of the 'M' class subs in its Special #9 in 2010 (Modelarstwo okr?towe
). The publisher doesn't seem to accept credit cards or Paypal so the easiest way to get a copy may be through GPM (GPM - modele kartonowe
The last post on page 2 here The Ship Model Forum • View topic - New polish magazine for shipmodeller MODELARSTWO OKRETOWE
has more info in English on the content of this magazine with images of the real M-class subs...