Are you looking to buy a new buck, or to introduce new blood on the female side?
Personally, I'd recommend getting a few menil does, rather than change the buck. It might take longer for the new genetics to have an effect, but the effect will be longer lasting.
Also bear in mind that the colour variants won't necessarily breed true.
I know a few folk who sell live fallow. I'll let you know if any menil stock crops up.
I have a couple of menil does to go from my park, but no way of capturing live.