I found a few steering wheels online. None are the simple version you are looking for. If you are handy you could make one yourself. You could use the plastic wheel from target and make your own mount for the car seat.

Hi 4tnee, I asked my Mother who owns an educational toy store in NY and she said she hasn't seen anything like this in a while. They carry a lot of nice wooden toys so I was hopeful, but no luck. Sorry I couldn't help more.

I found a little bit of a variety at amazon.com, in the toys and games catagory, under "toy steering wheel".

I have just ordered the sonic driver from one step ahead. I have not received it yet, however, it was the most realistic looking steering toy I have seen. It can also be used sitting on the floor or in a high chair at a restaurant. I had been looking for one for a while and when I saw this one, I ordered it 2nd day since we are leaving on vacation friday and have a 5-6 hour drive. The web address is onestepahead.com, the item # 13822.