Balun Component Sources in U.S.A.

Arrow.com   Ferrite Toroids (Fair-Rite/Amidon, Ferroxcube)

Search by manufacturer's part number. 

For FT-140-xx cores, search on:  59*002701 

For FT-240-xx cores, search on:  59*003801  

When I find time, I'll hunt out the Ferroxcube cores and see if I can find them there too.

Kent Coropration   Hollow Ferrite Rods (#31)

KF7P Metalwerks   Ferrite Toroids and Beads,  Misc. Hardware,  Heat-Shrink tubing

Kits and Parts dot Com  (The Toroid King)  A source for many common Toroids.

Mouser Electronics

(Important:  Amidon is not a manufacturer, they are a reseller.  Don't bother to search on the Amidon part number - i.e., "FT-240-43")

In this case you must search on the Fair-Rite part number, not the Amidon part number.

• FT-240-31  =  2631803802
• FT-240-43  =  5943003801 

Everett has compiled a list of Amidon vs. Fair-Rite part numbers.  (I'll post it somewhere and update here.)

more to come . . .