Hi Tony,
If the reference clock for your PLL is very periodic (i.e. stable frequency), then a 200:1 frequency divider in the feedback loop is doable. If the ref. freq is only tens of Hz, then it will take a long time (up to several seconds) for the PLL to establish lock at start-up. If there is a lot of phase/frequency jitter in your reference, you can steer your vco to the "average" phase/freq, but there will be a slow time-constant in the response of the VCO if the ref suddenly changes.
I did something like this once using the now dated (maybe obsolete) LM565.
As to making sure parts are still available, go to Mouser.com or Digi-Key.com, and look up the parts. Sometimes the OEM will publish "LAST ORDER" dates on their web site for parts that are about to be obsoleted.