When I wanted my LaFonda shell reupholstered,
my friend who did the work (Remnants, in Minneapolis) said "as long as as the edging was in good condition because I can't get the replacement edging..."

So, apparently, the plastic or rubber edging is the difficult (or impossible) component to locate.

Your La Fonda looks brilliant
Your La Fonda looks brilliant

Where's LRF?

He of all people would know. Perhaps it's a trade secret.

It is a auto trim and ...
It is a auto trim and comes in two sizes, we have tried on 10 chairs to use the original cord but it busted every time, what we use is a cord with a metal crimp in it, it should be able to be purchased at any auto supply house or upholstery supply or i could get it for any one that needs it, , you need around 7 ft of this cord comes in black shiny or dull we use the dull one, and it is 1/2 inch and very inexpensive We buy it in 200 ft rolls, and just crimps on perfect to the shell.
out of over 400 shells that we have redone in 3 years, not one customer has ever said they did not like it, Herman Miller completely gave up the uphoustery business on shell chairs in 1988, and with them went the original trim cords, untill we arrived on the scene no one seemed to recover the chairs at all, and
By the way, that is how i got in to this business, I bought a whole bunch of shell chairs for my office, and wanted them recovered and went all over to find someone who could do them, I ended up buying a auto shop that did boats, and fancy cars, and I added modern furniture, and that is how we evolved.