While third party desktop cradles are available for the HTC Titan and Radar (here's our review of the Mobi cradle), we haven't seen a massive distribution of the HTC cradles for these Windows Phones here in the States.
One such place you can find both the HTC Titan Cradle (CR S600) and the HTC Radar Cradle (CR S610) is over at Expansys USA. Not sure if these are European imports or are U.S. models.
Nonetheless, the cradle for the Titan can be found here and the Radar's cradle here. Both are running $38.99. If you know of any other vendors carrying the cradles, feel free to sound off in the comments.
Thanks, Clifton, for the tip!