I have some bookshelves that use machine screws and cross dowels to
hold their frames together. The machine screws are metric: M6 50mm
long, brass plated (antique?) over steel and (here's the real killer)
flat head (countersunk). As luck would have it, since moving house I am
missing some of the cross dowels and the screws, so I need to find
replacements. Ideally I would like to stick with metric fasteners, but
here in the USA that seems to be a tall order, so I could switch to
1/4-20 at a pinch.

I can find 1/4-20 cross dowels easily enough, but finding a source of
brass plated flat head machine screws seems to not be so easy.

Can anyone suggest a supplier who might be able to help (ideally
staying metric, but going the 1/4-20 route at a pinch)?
--
Peter Headland