Hamfests.
Radio Shows.
Local radio clubs (there is at least one, often several in every state).
Craig's List.
Put up a want-ad on Craig's List.
Yard and Garage sales - especially in older neighborhoods.
TV Repair shops - Amazing what some of them have sitting in the back room - *IF* one still exists in your area.

And if you are anywhere near/around Kutztown, PA in May, the Kutztown Radio Show will have what you need at reasonable prices.

Peter Wieck
Melrose Park, PA