Best functional training sportshop in Köln?

Hi there,

summer is back and I need get on shape.
Where could I buy functional training equipment? More specifically gymnastic rings (Turnringe).

I'm quit disappointed by what Decathlon offers, went in two Decathlon in Köln and couldn't find one. Also Sport Tieldje didn't have any gymnastic rings. When I google Sportgeschäft Köln, I mostly get sportswear shop results, which is obviously not what I'm looking for ...