They're distributed by RC-Disco, along with Xray and Hudy. The KO 2.4gHz range is meant to be far more reliable than the Futaba 2.4gHz, despite being made by Futaba. Can't help feeling that if Futaba can do it for KO, why can't they do it themselves?
All receivers can be used with 6V Rx packs (or a Lipo with a regulator). I have NEVER come across a receiver without a battery port, or the ability to be powered by a seperate pack.