Go to your stockpile and delete the SINGLE sections that have silver in them (and disallow silver from your stockpile - don't let your colonists move the silver).
Voila, you'll begin getting traders again.
As it stands, for some odd reason, the more wealth you have in your stockpile, the less traders will come.
Voila, you'll begin getting traders again.
As it stands, for some odd reason, the more wealth you have in your stockpile, the less traders will come.