Here's the relevant text fro the SRD:
A monk fighting with a one-handed weapon can make an unarmed strike as an off-hand attack, but she suffers the standard penalties for two-weapon fighting. Likewise, a monk with a weapon (other than a special monk weapon) in her off hand gets an extra attack with that weapon but suffers the usual penalties for two-weapon fighting and can't strike with a flurry of blows.
Flurry of Blows: The monk may make one extra attack in a round at her highest base attack, but this attack and each other attack made that round suffer a –2 penalty apiece. This penalty applies for 1 round, so it affects attacks of opportunity the monk might make before her next action. The monk must use the full attack action to strike with a flurry of blows. A monk may also use the flurry of blows if armed with a special monk weapon (kama, nunchaku, or siangham). If armed with one such weapon, the monk makes the extra attack either with that weapon or unarmed. If armed with two such weapons, she uses one for the regular attack (or attacks) and the other for the extra attack. In any case, her damage bonus on the attack with her off hand is not reduced.
The last part of the second paragraph does kind of imply that monks cannot combine two weapons with a flurry and get both an off hand attack and a flurry.
I don't think rapid shot helps here because it takes an entire round for the kama to return when you throw it. If you had several returning kamas and Quick draw, that could be a different story.
Your concept of off-hand is off too. Monks can indeed use various parts of their body when making an *unarmed* attack (they can mix punches, kicks, elbow strikes and so forth) without penalty. But this does not give you an extra attack per round.
If you are wielding weapons, though, this does not apply. A monk wielding two kamas can still use his more favorable unarmed attack bonuses, but he does not get to ignore penalties for two-weapon fighting and ambidexterity when fighting armed.
If you are a 20th level Monk, you normally get 5 attacks per round (using unarmed BAB) So the number of attacks you should get with two kamas in a flurry is:
5 (Monk attack rate) + 1 (flurry)
If you flurry, all your attacks are at -2:
If your BAB is +15, your attacks would be at:
+13/+13/+10/+7/+5/+2
(Your extra flurry attack is at your highest BAB.)
If you have a non-monk weapon in your off hand, you can't flurry, but you can still get an extra attack with the off hand, with the normal two-weapon-fighting penalties. If you have all the feats and the weapon is light, the attack numbers wind up to be the same (-2 for primary hand, -2 for off hand).
Someone please correct me if I'm wrong (like you won't anyway, right?).
Edited: Fixed bad numbers