Here is some further info:
Concord Components (800) 871-1749
Their latest catalog lists the SBL-1 and RMS-1 (surface mount)
mixers for $4.25 (or 10+ for $3.75).
Johnson Shop Products (408) 257-8614 or fax: (408) 253-6288
P.O. Box 2843, Cupertino, CA 95015 email: firstname.lastname@example.org
This is one of my favorite parts sources. They don't have any
mixers listed in the current catalog, but I have gotten some
TFM-series units from them before. They also carry a lot
of toriods, coils, IC's, hardware, Litz wire, etc. All depends
what they have gotten in as surplus recently. And the good
news: no minimum order!
Hope this helps.
- Dale WB6BYU