One eight channel [binary only/contact-state] is http://www.selinc.com/sel-2505.htm Rock-solid reliability.

You might check www.opto22.com. ; First step is to convert your inputs to digital and then multiplex them over a single serial port, RS-232 or RS-485.  The conversion back and forth to fiber is straightforward.  There are a lot of converters to do this on the market.  

You can do this with a wide variety of programmable logic controllers as well.

For fiber, you should plan on a dedicated pair of fibers.

Good luck, and hope this helps.  

As far as the comms part of the question, I used a pair of modules from Phoenix Digital Corp. for fiber-based communications from PLCs to Remote I/O racks on an A-B PLC-5 system. As far as a stand-alone system goes with I/O at either end, I don't know. From what I understand, Phoenix Digital makes products to serve a wide variety of industrial control platforms, but the user has to supply the intelligence at either end to convert to/from I/O. Check out their website at http://www.phoenixdigitalcorp.com
Maybe they have something you can use.

A company called Eurotherm makes a product called Link. It uses fiber optic cables to connect various modules together.  I have used it a number of times. They have analog modules, digital modules that have both inputs and outputs.  The Link I style uses 24Vdc as a power supply.  The modules not only can handle the analog (5 ins 1 out) and digital (12 in or out) signals but also are fully programable computers with a complete set of function blocks available and can operate as a fully functional control system if you want. The modules are fairly small and mount on DIN rail. They also have a Link II system which is much more powerful and uses 120Vac and plug-in digital (16 in or outs) and analog (8 in 2 out) cards. Call 800-279-0102 for more information.