Hello,
it's been quite some time since you posted your question, but maybe an answer is still helpful...
It's highly improbable that any 9 speed shifter would work with a 6 speed drive train - as I see it, you have basically got two options:
A) If you use drop bars, install bar end shifters (like
these ). They can also be used with 9 speed drive trains if you don't need the indexing.
B) Try to find a clamp that substitutes the bosses on the down tube (
example ) and use your current shifters...