beis hamikdash - the lechem hapanim was NOT chametz - where is the source for this?

We had the discussion what happened with the lechem hapanim on Pessach and the answer is that it was NOT chametz. Where can I read up on this fact? There were actually only TWO instances of chametz in the Mikdash - 1.shtei ha'lechem on Shavuos and 2.challos of the korban Todah.