Dianne, good luck in your search. All I found was a Dick and Jane print with a little girl riding a trike.
http://www.jandofabrics.com/proddetail.asp?prod=djn0002
http://www.jandofabrics.com/proddeta...?prod=chi30532
http://www.jandofabrics.com/proddeta...prod=chi000101 This has a boy on a trike, but is out of stock. You might could email some stores in Australia and see if they have any.
A possibility you might consider is to use a photo or clip art of a trike and print it onto fabric. I used several search engines and couldn't come up with anything except the above.