Hi Alex,
if I recall it correctly you are living in Finland.
Therefore I am not sure if Werner's advice will help you. Even in Germany it is becoming increasingly difficult to find a locksmith who does have the necessary unmachined keys on stock (sorry, I don't know the correct term in English - in German it's "Rohling"... maybe "slug" or "blank" is the right word? Anyway: I'm sticking with "blank" for now).
@Werner: do you know a reliable source for suitable blanks? Could be helpful for quite a lot of us.
First of all you should contact your local locksmith. Maybe you are in luck?
Next (if all you get is a mighty shrug and a week grin from your local locksmith) you could contact a "Schluesseldienst" (key service) via the Internet. I guess your key is a "Neiman" (the original manufacturer), so you should include "Neiman" in your web-search. Hopefully you will find a company in Finland.
If not I recommend to concentrate your search on "Schlüsseldienste" in Germany or Austria. For example I found this one mentioned in the "Zuendapp Forum" (
http://www.zuendapp.net/forum/index.php?topic=13012.0):
Konrad Schlosstechnik GMBH
Brauscherweg 2
63897 Miltenberg
Tel.: 09371 97740
Fax.: 09371 977477
e-Mail:
info@konrad-gmbh.de
Please be aware that this is quoted from an old post (from 2008). No guarantee that you still can get a key from this company - it is just one example I did find using the search term "neiman schlüssel nachmachen" with Google (i.e. "neiman key reproduce").
Or you could do what I did: browse ebay for some time, searching for "Neiman Schlüssel Rohling". Be aware that you will get (at least on German ebay) a lot of hits, but that unfortunately most of them are for blanks which do not (

) fit your own key. You have to be patient and you have to look very accurately to find the right/fitting blank.
After you (finally!

) found the right blank all you need is a set of small files (in German these are named "Schlüsselfeilen" which is "key files" - I hope that's the right translation). The profile of your Heinkel-key is quite simple and (assuming you know how to use a small file) it is not complicated to make/file your own copy from the purchased blank.
BTW: I did pay 8,66€ for one blank. That's not cheap - but better than loosing the only key and changing the whole lock afterwards.
So let me summarize: it will not be "a piece of cake" for you to get a second key. But it is no "mission impossible" either.
Bye,
Bernd