Try Northeast Aerospace (PO Box 367, North Andover, MA 01845, (978) 725-8085) for Tridair fasteners.  I bought them in 2006 in small quantities for $7.75 (CA 1820-1 studs) and $8.85 (CA 18157C receptacles).  I don't know if these prices are competitive with others you've found or a group purchase as I've not followed this thread for long. The company was super to deal with: they had everything I needed in stock and delivered within a few days of my order.

Good luck...Clark Still (N750S, KPOU)

PS - As cowl fasteners, these are great!

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