Hello!
I think that all WMO tecnical notes are now available in digital form. I contributed to several, and got pdf versions, including some old ones that were scanned. Please explore their (website
http://www.wmo.int/pages/prog/wcp/agm/p ... notes.html), drop them a a line or ask for the help of the head of the Agromet division Robert (Bob) Stefanski, whose email address you can find on the website of WMO too.
Good luck & regards
R.