Where can I find parts for a broken wheel hub assembly?
I must, unfortunately, say nowhere, probably. I mean, this is an old, discontinued model and the brand from the time of its release went through quite a huge rebrand with all the stroller models changed in between. At this moment, the iCoo brand doesn't even exist, it completely went under the Hauck brand.
There's no place to get spare parts for this pram/pushchair except maybe by going through classifieds and finding someone selling the same, functional stroller either as a whole or at least for parts. I mean, you can try to contact Hauck directly but I am pretty sure they won't help you with this at this point.
My suggestion would be to move on and get a newer stroller, even if maybe this grew on you so much.