As it has been hinted before I agree that you don't seem to really know what gray market is. Gray market requires a fair amount of infrastructure and resources that extends far beyond what your expected level of commitment is.
First you need your supplier chain, this requires not only money ( a lot of it) and a guaranteed stream of purchases so you get any priority at all on pieces that may be on high demand, but also an established trust
Second you need a buyer pool. That is not easy on this competitive market because you are not established and have no history as a dealer. Much less a gray market dealer.
Third you need infrastructure and resources for storage, packaging, shipping, insurance, and a resource for authenticity and validation of watches both outgoing and incoming. (Don't forget about all the returns you'll be handling). Remember; to be competitive you will have to supply your own warranty as there is no factory warranty on gray dealing. You need to be licensed to carry brand warranties. Sort of like franchising. That is where the margin of discounting is on gray versus authorized dealership.
You need marketing, branding, and costumer care (because a gray dealer is a dealership not a person)
And all this while you have a full time job and just want to get your hands on some watches and learn. Want advice? RUN.
OR....
What you are talking about is getting information about how to deal on watches, flip them, sell them, source them. THAT IS NOT gray dealing. It is dealing. Period. You may be able in time to source new watches...there is no shortcut on that...you just have to deal enough that you become part of a network of buyers and suppliers.
And.Then.You. Hassle.
Want a first lesson? Go to the seller section of this site. Both on private watches and dealers, and read through about 200 posts. Not just the posts but the comments....see what moves and does not move, see what the expectation on offering is, See what the expectation from the buyers point of view is. It is all there. That is the world you're aiming to enter and you have a window right into it if you want to take the time to read through it.
I personally do not see why anyone would train you to become their competition or take their buyer or supplier list away from them. But, hey, you never know until you ask.
There where years where between cameras and Watches, between selling and buying, I had transactions worth more than 6 figures combined. I never saw it as a business and lucky for me, I think I came out about even at the end of the day. Lost on many, gain on some. I would say the initial output on my end was considerable before I gained some balance on my flow. I enjoyed it; Mostly because nobody mentored me. What is the point of a hobby and passion if it does not imply a hefty time and effort investment?
Good luck.