NOTATIO

What paper sizes are available in the US for orchestras to print parts themselves?

My guess is that Letter is not an option.

No, the smallest we would accept was 9X12 (inches) with a 7mm staff.

Preferred size was 10X13 (same as a standard Kalmus part) but we had to have that custom cut. However, many professional orchestra libraries use this size.

9.5X13 is also common.

I think G. Schirmer used to use a very large size, around 11X14, but i don't think that is the case any more.