Best ways to poach mages...

[Gregstrom]

You may seek them with thimbles
You may seek them with care
or pursue them with forks and hope.
You can threaten their lives with a railway share
and charm them with smiles and soap.

Alternatively, try remote assassination spells. Earth Attack, Infernal Disease, Ashen Angel are examples thereof. If you're really intent on only getting mages, spam flying monkeys at a province first to clear out all the non-mages