The pro and con of Sinar is that there was just so much stuff made that you need a "code" list of specific components dating to the relevant
decade or whatever when particular models were made. Minor repair parts are a different story. In the real world of today, it is often cheaper
simply to buy a whole major component or even a separate camera for parts than to acquire a piece from the official distributor. This tendency has of course wreaked havoc on the traditional marketing program of SinarBron, which was $$$$$. But nearly everything in the Sinar system is interchangeable to some degree. You can get in trouble with bastardized setups of mismatched front and rear standards, however, and when suspicious of a particular seller its best to ask around on forums like this or the Large Format Forum from existing users.
Camera stores have largely dropped Sinar along with most other monorail systems simply because they can't compete with the glut of product on the used market. A bit of patience can make all the difference in the world regarding what does come up for sale. Some of the
camera being sold off by retiring or reequipped studios can be barely used, while others have been pretty mauled over the long haul. So
it helps to understand just how old a system might be... "P"cameras, for example, were made for a long time in several configurations, while
"X" cameras are all relatively new.