The yellow Huna is apparently a prototype - so while its exact origin may not be known, it can be safely deducted that someone involved in BIONICLE's early production gave it away to a fan or otherwise parted with it so that it could find its way into the community. I haven't heard of a red Huna, though. I think there was a dark red one among the prototypes that were given to BZPower, but that's the closest thing I can think of.
The white Huna actually came from calendar bags in a European country (possibly the Netherlands, if I am remembering correctly. Unfortunately, I can't check since the archive is gone), alongside the brown Komau. So their origin is known, although how they ended up in the calendar bags is a complete mystery.