Recommended parts sources for replacement & repair

For general parts sources check out the following:

McMaster Carr
    Industrial supplier that carries a wide variety of screws (phillips head, socket cap, flat head socket cap).  Minimum order numbers apply but prices are good.  Excellent website with online ordering, detailed catalog, pics and specs.

Online / mail order guitar parts supplier.  Been in business over 30 years.  Though not Steinberger specific, they sell a wide range of general items for 'berger owners: electronics, pickups, knobs, screws, tools (like wrenches) and an assortment finishing & maintenance supplies.   

Ed Roman / World Class Guitars
    Though Ed is deceased his shop lives on.
They list a great many parts on their website but reports are they don't have everything in stock. Worth a shot though.

Here are some other specific ones: