While you're searching in the US, maybe consider looking in Great Britain at
http://www.eurospars.com/sparcraft/sparcraft-parts/.
From their web site:
As main UK agents for RDM Sparcraft we can supply any parts for Sparcraft masts, booms, spinnaker poles, vangs, deck equipment, backstay tensioners, rigging and any number of other parts.
We hold a large stock in Plymouth and try our very best to ship stock parts within 24 hours of order.
When making your enquiry please have as much data regarding your yacht/mast as possible. We will need year of build and hull number and if your mast has a number stamp that will really help..
Note that number stamp will normally be found at the sail entry position. [Ed.: this is interesting. I'll have to take a close look at my mast]
Isomat and Francespar masts were the two large French Spar manufacturers of the 70's and 80's and there are still a large quantity of these masts spread far and wide around the world.
These masts were built for many of the large european yards such as Gibsea, Jeanneau, Beneteau, First, Dufour, Island Packet, Malo and many others.
Isomat and Francespar were merged and re named to form what is today's Sparcraft. As Sparcraft agents we have many of the original mast data and plans for this era of yachts. We have the technical knowledge to service these masts. We can still supply many of the parts needed by customer to keep these mast sailing for many year to come
