Most of the parts for this product are pretty much "off the shelf" and can be obtained through DigiKey, etc.. There is one very large and ugly exception, however. The converter circuits (A-D, D-A) contain a "7th order lowpass Switched Capacitor Filter" chip (EG&G-Reticon RF5609A) which is virtually impossible to get anymore. To make matters worse, this is a fairly common part to break down in the product. One of the reasons I no longer service this product is because I got a couple of systems in for repair and invested sometime on the units before I found out they were no longer available. And when they were available, they weren't cheap: $12.55 each! A real drag.
At one point I spoke to someone who had found a replacement part but the pin-out was different. Based on the very tight package of this product, I consider it a very risky proposition.
This is the AD converter used to decode the switches on the unit itself and the remote. I found a listing for them on Arrow electronics web page (search for ADC0804) but you can probably get them at any serious parts distributer.