I'm also interested in locking a transmitter frequency to stable reference.
The ICOM FR-6000 repeater which I use has a TI LMX2352 PLL which relies on a 15.3 MHz Crystal Resonator, CR-826 type.

It appears that I might be able to replace the crystal with a reflock board (Link below), with the reflock generating the 15.3 MHz.
http://www.qsl.net/ct1dmk/reflock.html

Here is an example of a ham reflock'ing a yaesu 817 all-mode radio to a 10 MHz reference input
http://www.vk3hz.net/riglock/FT817_External_Reference.pdf

The 10 MHz reference signal can be from a Rubidium Oscillator or from GPS Disciplined Oscillator, both of which are available from eBay.
The Trimble Thunderbolt is a common GPSDO. Some good general info is on John's web site: http://www.ke5fx.com/tbolt.htm

73,

Randy - VE3RWN / W3RWN