New wheels and tyres were ordered from Aliexpress:
https://nl.aliexpress.com/item/100500...
During mounting I came across 3 challenges:
1. The hole in the wheel mount was just a couple of tenths too small, I used a 3mm drill to make it fit.
2. The front tyres were touching the steering bar, which led to friction. Placing a ring on the hex wheel nut moved the wheels out just enough to solve this.
3. Some wheels were wobbling. thin plastic disk between the wheel holder and the wheel to mount it on a slight angle, which virtually eliminated the wobbling.