My understanding is that they have been released, but I've not looked for any as I load for .45's.
They are available packaged as muzzle-loading projectiles packaged with sabots......
I got my first FTX's for my M94 Win. .45lc by buying some of the ML packaged bullets (250gr .451").
Try Graf's and Midway as they have been listing the other FTX calibers as available (ie: .308, .35, .323", .45/70, ect.)