Well despite your wishes, these things come in as a SET, and with these days throw-away electronics, I doubt the vendor will sell you just the controller. Look, where else, eBay. If you are lucky somebody has a set with broken speakers but working controller.
What is this "controller" anyway? a cross-over? an amplifier? Maybe you already have an amplifier and can use the speakers as passive? Maybe you don't need the "controller."