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
    If you absolutely, positively need something Steinberger, Ed Roman may still have it.  Since Ed's passing in 2013 their stock has dropped considerably but they still have many parts listed on their website.

Here are some other specific ones: