Check Dwyer Masts (Look under parts and accessories on the home page)
Or if you are into racing and want a tapered mast, try Proctor masts (http://www.proctormasts.com) in California or Cape Cod Shipbuilding in Massachusetts for Zephyr masts.
For used masts, keep checking around with local Day Sailers and here on this board.
Dear Phil & Chris,
Check with Rudy at D&R Marine/O'Day Boats. His web site has prices for complete mast set-ups and basically any daysailer part you may need. Rudy & Co. are very helpful and friendly too.
Len Phelan