We get them occasionally, I'm having a problem with earwigs now. They also like the wet conditions. We have a patch of ground between the deck and privacy fence near the AC unit and it never dries out, EVER! Moss grows there, not grass. I think that's where they are coming from and they just sneak in around the foundation.
There are all kinds of things on the market to get rid of silverfish and any other little critters. Google silverfish killer, you'll get a multitude of options.