I've been a trainer for over 5 years now but have always just trained my own 2-4 horses as a hobby/2nd job. I am 3rd generation horseman as my dad and grandpa did the same thing. I always do well with the horses i train and I've recently been kicking around the idea of doing it full time and I am unsure how to pickup owners.
Getting close to your drivers as boots on the ground hearing info all the time, maybe offer them a finder fee, guaranteed drives..
Not sure where you live, but you could start a conversation with trainers in other jurisdictions about transferring horses to locations you're stabled. Sharing...
You could follow the suspended trainers list closely and pitch owners as soon as their trainer is suspended for a great length of time.
Go to auctions, hang around the more exclusive parts of the track, get very friendly with race secretaries.
Start a fractional ownership advertising and put the word out so they can come in for a piece to start, it doesn't ave to be 1% min but 10%.
Keep your ear to the ground and see if any trainers are retiring.
You can keep your identity concealed here but what about sharing your general location i.e. state, expertise i.e. young horses, improving claimers, trotters and or pacers...