I'll need a center frequency of about 5KHZ with the ability to vary the frequency 10:1.The gray market or eBay is probably your only hope. What frequency range were you planning on? The alternative is an oscillator with a varactor diode.
Or maybe these guys:
http://en.wikipedia.org/wiki/CEM_and_SSM_chips_in_synthesizers
Sadly, most of the chips those guys made are now very hard to find... I bought 10x SSM 2040 in the early 1980s for a project that never got finished. That device become so rare and sought after in recent years, that I got $40 each for them a couple of years ago!Or maybe these guys:
http://en.wikipedia.org/wiki/CEM_and_SSM_chips_in_synthesizers
by Jerry Twomey
by Robert Keim
by Jake Hertz
by Duane Benson