I think most LNBs that have a crystal should be lockable to an external ref. http://www.pabr.org/radio/lnblineup/lnblineup.en.html#
As of now, I have successfully injected a 25M reference into the 3566 marked chip found in many chinese LNBs, and also the RT320M, which is a twin LNB chip. I am pretty sure it can be implemented in quad LNB chips aswell.
It is just a matter of removing the crystal, and injecting your reference with a simple diplexer (LC series and LC parallel) into one of the crystal pads, just like this http://www.hybridpretender.nl/single.pdf
Also, something that is not covered in that document, and I had problems with, is cutting the wiggly line going to the voltage regulators and adding an SMD inductor. That wiggle line is enough inductance to block the IF going into the regulators, but is not enough to block a 25M signal, and the decoupling caps at the input of the regulator were eating all of my 25M reference preventing the LNB from locking. Once I added an external inductor (820 nH IIRC) it locked just fine.
Just passing by to leave pictures of the Dual LNB I modded, as I did not have them when I first replied to this topic.
Recently I had to re-open it and solder an additional 47 ohm resistor to properly terminate the 25 MHz LC series at the crystal pad, in the hope of solving some issues with noise from the bias supply appearing in the downconverted IF spectrum.