Hi and welcome!
Use the trusted dealers, there's 24 to choose from in the dedicated section: https://forum.replica-watch.info/forums/trusted-rep-dealers.147/
Use only those links, never Google them as scam sites are all over the place.
Tudor BB's specialized factories should be ZF and V6f, but check first in the tudor section to confirm this info, I haven't researched the gmt specifically yet. You can use Google to look for info, add "...site:forum.replica-watch.info" to your research and you'll be rewarded by a lot of info right from rwi.
Happy hunting!