You could just get a a copy of your blue key so you have a back up. To get a new master key will cost over $1000.... If you can find a key cutter that has the right machine that can replicate your blue key it will cost around $100. Good luck.
I think that Vespa keys are compatible with Fiat keys so it might be worth checking with a Fiat dealer.
The key that can be copied from a non master key will obviously not be a master but it will be a totally reliable spare.
If I'm any judge of life I can almost guarantee that your original master key will turn up as soon as you've paid for a copy.
Hi Jo, I bought a GT 200 last year that came without the blue key and only a single brown key. I looked into buying a Vespa blank key but didn't and instead arranged for a mobile locksmith to supply the blank and make a copy from the brown key. I've put the brown key aside in a safe place and use the new key (which is blue in colour!). It is a lot easier to create a duplicate from a brown key now than when the Piaggio anti theft system was introduced in the early Noughties. The mobile locksmith charged like a wounded bull, over $200 for the blank and programming but did come to me. You should be able to save yourself the premium charged for the visit by going to a good locksmith. Roberto has the name of the one I used and I do know that he is currently tasked with fixing a scooter for which both the blue and brown keys have gone missing. If your local locksmith can't make a copy then ask an auto electrician or Roberto where to go.
Glad you have some options of locksmiths. The Master Key (Brown Key) holds the computer chip for your vespa, that is the importance of it Jo. This one can't be copied. Hopefully you do find it one day.
Jo, the biggest advantage of the master key is that you can use it to program blank blue keys.
You can do it yourself on your scooter.
It means that you can purchase a blank blue key and have it cut anywhere and then program it yourself.