Sorry I can't answer that directly as there are millions of possibilities. The most simple is either a kit or stuff from a shop that provides stuff for RC vehicles. As you didn't write where you are from, it is difficult to advise a specific webshop as not every webshop is shipping everywhere....But I can give you some inputs to get your brain started.
Well, to select some wheels you need to ask yourself some questions:
- How big shall the robot be?
- What speed shall it achieve?
- What terrain do you want it to drive?
And for the motors you need to do basically the same.
- What are the physical dimensions of your wheels?
- What payload do you want to add to the robot?
- What size is your robot?
- What power sources are available / What is the power rating of your battery.
And generally:
- What is your budget?
Hope this helps for starters.
Best