You're free to like a name wherever it's put, but personally I'd never be able to see
Tristan as a girl's name. It's too bound up with the legendary knight - to me, naming a girl
Tristan would be on a par with naming her
Arthur or
Lancelot. They're all Round Tablers together.
I love and adore it for a boy, though, and am slightly disappointed that a) it's got popular and b) I can never use it because my sister's called
Isolde.
How about (sorry for any repeats):
Tristan RayTristan GabrielTristan AlexanderTristan NicholasTristan LukeTristan JuliusTristan RaphaelTristan LeeTristan BlaiseTristan AlastairTristan DouglasTristan JamesTristan KaiTristan MichaelTristan AnthonyTristan DiarmuidTristan RiverTristan Niall
Any you like?