I would like to enquire to hire a 9 seater mini bus at Schiphol Airport in Amsterdam
When you conduct your search you will find it here:-
Type only "AMSTERDAM" in the search machine. From the drop down menu you can choose "SCHIPHOL" then at the top of STEP2 (above the individual car photos) is a scrolling left to right car type filter, where you can filter the results by car size, for example 7,8 or 9 seaters. A credit card is required.
If no car photos are displayed, then adjust your date/time as not all locations are open weekends or out of normal business hours.
If possible use a laptop,tablet or PC rather than a mobile to conduct your search.