Try www.popularcommunications.com... I seen an article in there about them.

Article was in May 2003 Popular Communications magazine its on page 8 and
the person who wrote it is Bruce F. Elving. Ph.D.

DXing Those "Secret" Subcarrier Signals On FM

How To Turn A Radio Band Your Neighbors Don't Know Exists!

More Info can be found at http://members.aol.com/fmatlas/home.html ---not
sure if it still works worth a try though.

Or you can write for a printed catalog to P.O. Box 336, MN 55733-0336


Good Luck