maybe they go elsewhere but i never saw any windsurfers in cairns when i lived there. Bear in mind that Cairns has essentially no wind in summer and then the tradewinds do blow March - September but this is steady winds 12-18 knots. Good for kitesurfing but just not quite enough wind for windsurfing unless you longboard or have a huge sail. Foiling wasnt really a thing when i lived there.
Maybe Port Douglas has windsurfers.... more wind.

Don't know about hire, but when I've visited Cairns in the distant past, I sailed Yorkey's Knob a few times (some 20 minutes' drive north of Cairns).