Hi Winnie
I think Zooplus don't have them as they are such a big seller. They seem to go out of stock as soon as they come in! Personally, I love the Karly wheels as they are really well made (definitely no nails in these ones) and our robos love them. They are so quiet, you can't actually hear them spin - all you hear is the pitter patter of tiny feet on the wood (literally) which is quite sweet really.
I like them so much I decided to sell them in my shop. I happen to have a couple of the 29cm size in stock if you are interested - not quite as cheap as Zooplus (if only I had their buying power!
but a lot cheaper than Amazon when you add delivery on too.
See link below.
Natural Wood Exercise Wheel from Karlie Wonderland