Yes, break the magnet and you have to get the entire part from Triumph.
Ridiculous policy. On a Suzuki SV650, you can get replacement magnet alone for $18.
There was indeed one on EBay the other day I noticed.
(Edit: I see you're in Poland though - check EBay European sites)
Here are the ones on EBay US - you can maybe ask if they'll ship to Poland.
Speedo Drive #1
Speedo Drive #2
Speedo Drive #3
Incidentally the reason it happens is your wheel wa not installed properly - the little 'tangs' on the drive ring that floats in the wheel hub need to properly engage the detents in the magnet.
Did you or a service agent have the front wheel off recently?