TCXO source

Search under crystal in "Business Equipment/Test and Measurement" -- there are always sellers of HP TCXO's -- usually these are pulled from HP5328 frequency counters with option 10. Occasionally you will see an HP5334 with same. Lastly, some HP3586's (Selective Level Receiver) have a very stable oven - in this series the option is 004 -- all the above use 10 MHz. You can even buy a rubidium frequency source on EBay if you look frequently enough.

You can also try www.hamtronics.com or www.isotemp.com.
 
TCXO and PLL discussion in Analog Dialogu

The new issue of Analogue Dialogue has a lengthy discussion of PLLs and a brief mention of tcxo's -- points out some of the problems using A-T cut crystals

http://www.analog.com/library/analogDialogue/archives/36-03/pll/index.html

if you're wondering where all the low-noise ampls are coming from , read the article on Ultrasound in the same issue.
 
I snipped from the article below:

<em>Q. I’ve selected my synthesizer based on the output frequency required. What about
choosing the other elements in the PLL?
A. Frequency Reference: A good, high quality, low-phase-noise reference is crucial to a stable
low-phase-noise RF output. A square wave or clipped sine wave available from a TCXO crystal
offers excellent performance, because the sharper clocking edge results in less phase jitter at the
R-counter output. The ADF4206 family features on-board oscillator circuitry allowing low cost
AT-cut crystals to be used as the reference. <b>While predictable AT crystals cost one third as
much as TCXOs, their temperature stability is poor unless a compensation scheme with a
varactor is implemented.</b></em>

I have one of those 10e-9 ovenized sources that I run my counter and synthesizer from.