Thems are easy, they are basically machine screws. It's the long skinny ones that are hard to match.
I once went to a fastener store and he basically said that nobody makes thpse kinds of screws (thin guage with wide thread pitch, for plastics). They sell virtually all kinds of fasteners and the place looks like an industrial warehouse. He did say the only way to get them would be custom made, and that would involve ordering some godly number (I think at least 5,000... or was it 50,000). The closest match are probably the fine pitch sheetrock screws but the head design is wrong and the point needs to be ground off.
Apparently, boombox manufacturers custom cut screws to their specifications and they were not standard off the shelf spec'd screws.