What is the good source for balsa wood. I tried to check the LHS and the 1/16 x 4 x 36 (Midwest) sheet is about 33 - 40 grams...way too heavy compared to 12 grams (required weight per recommendation).

So my question is, what is the best source to get contest balsa sheeting? I am thinking to order 100 sheets from tower, pick them after using scale and then return the heavy one back to tower? Is this works OK? Any online source, which only sells contest balsa?

Thanks
Srikar.