You might have luck spreading some diatomaceous earth around where you see them skittering. It is the fossilized remnant of ancient sea creatures (but looks like powder.) Apparently at a microscopic level DE is very sharp and can rip apart anything like ants, termites, mites, and I don't see why not silver fish... You can buy it at your feed store for pretty cheap. Not sure what else I'd suggest. I have no idea if silver fish would fall for the borax-tainted sugar water like ants do? You could look it up I suppose.