They're definitely kept, but not by many. Ivor at North Cornwall Aviaries used to have some smaller species and aracaris to my recollection. Oddly enough though, Hornbills seem to be more common. I think C&J bird brokers have advertised them in the past, and there have been occasional adds in Cage and Aviary Birds, but I don't know of any specific breeders otherwise.
Ivor at North Cornwall Aviaries used to have some smaller species, Aracaris and possibly Sulfur Billed, but they do tend to be quite rare in UK keeping. Hornbills, oddly enough, seem more common. There are occasional individuals advertised in cage & aviary birds, C&J Bird Brokers for instance have sold them before.