Badger:
well, the 21 after his name was the year of his birth. "Optingenstrasse 35, Bern" was where he lived and was stationed. it may be pushing it that he's still alive, but do what i did and try this international phone directory:
Die Schweizer Suchmaschine - search.ch
i found my K31's owner with it. wrote to him and got a response. one of the single coolest things i've ever had happen to me.
i was lucky in that my rifles' owner is the only guy in Switzerlandwith his name so it was pretty easy to just send him a letter. the letter i sent was from here:
Letter to the one on the Tag. in General Discussion Forum
your guy's name is Italianso you might try sending out the Italian one as well as an English copy
hope you find what you're looking for.