In the US they seem to be under one umbrella:
Kenko Tokina USA, Inc.
and when you look at the individual sites:
http://www.slik.com/ (853 Kayama, Hidaka City, Saitama, 350-1231 Japan) +
81-42989-0990 http://www.hoyafilter.com/ (KT Nakano Building, 5-68-10 Nakano, Nakano-ku, Tokyo 164-8616, Japan) +81-3-6840-3037
http://www.tokinalens.com/ (KT Nakano Building, 5-68-10 Nakano, Nakano-ku, Tokyo 164-8616, Japan) +81-3-6840-3037
http://www.kenkoglobal.com/ (KT Nakano Building, 5-68-10, Nakano, Nakano-ku, Tokyo, 164-8616, JAPAN) +81-3-6840-3228
very similar Hoya and Tokina even have the same phone number.