Moss will never grow underneath you feet, I suspect. Good on you for jumping right in, so soon after its aquisition.
I have wanted a Brilliante or a Super Brilliante for some time now. Argueably, it's perhaps the best clarinet made when it was made.
That key is going to take some real searching.
If you can find someone nice enough to do this, (and who has the same key) see if they will make a 3D scan of it (or send it to you so you can) and put it in a file for you. This way, you can recreate it, do a reverse casting of it, and cast it in nickel silver.
I just attended a hands on seminar/workshop on 3D reconstruction printing for hard to find and obsolete musical instrument parts. The above proposal may sound expensive, but it's surprisingly affordable, and will soon become the standard, I believe. The main focus was mouthpieces (refacing, reconstruction, and the use of T-glase--a special polymer product that is FDA approved for oral use, but they also covered brasswind valves, and a lot of other things as well) As an aside, I can now do a basic refacing on any mouthpiece (as soon as I purchase the measuring tools, that is.)
Regards-