Hi, Jelena,
We talk about spare and replacement parts in this article, I definitely recommend reading it.
The things is, you cannot "just" buy it in a shop or online shop, it's a thing that needs to be ordered by a distributor or sold/provided by the manufacturer, in this case, Tutek.
If not stated otherwise, you shouldn't normally put parts of a certain model to a different model, even if from the same brand, as it was not tested to be used like that and can be potentially unsafe. Still, Tutek and other Polish brands make the attachment systems as well as carrycot very similarly, so it might fit other Tutek chassis with the same type of click-on attachment.
So, read the article. Try your options. And, if nothing works, you can still browse classifieds to find the same or very similar Tutek model that you'd buy for parts.