U.S. parts guys (the good ones) DO have access to worldwide parts stocks. More than once when a part wasn't available in the U.S. my parts guy was able to find one in Europe and get it shipped over. However, there are parts that are restricted for ordering, usually parts that deal with emissions, safety etc. For example a U.S. dealer can check status on the euro headlights but CANNOT order or have one shipped to the U.S. UNLESS they can verify the VIN number belongs to a european car legally registered in the U.S. Usually this is for diplomat's cars.
Don't know if the key would be under this or not, nor do I know if the euro chip and immobilizer is the same as U.S. cars.
Well, I emailed a parts guy at the Mercedes dealership in Warsaw. In my broken Polish. Hopefully it makes sense to him and hopefully I get an answer. If he can order one for me, I will test it out and if it works, I will become a "Keyler" for us US guys and start a "bidness"...