They are called bumper stops.
http://www.iboats.com/Windshield-Door-Pads/dm/*******.659129948--**********.615671936--view_id.40194
http://www.real4wd.com/zedSuite/catalog/partdetail.aspx?partno=12338824
http://www.google.com/products/catalog?hl=en&q=rubber+bumper+stops&bav=on.2,or.r_gc.r_pw.&biw=1536&bih=762&wrapid=tlif131168538928710&um=1&ie=UTF-8&tbm=shop&cid=9862157869239492575&sa=X&ei=N7suToaLLaXW0gGW1uHeBw&ved=0CFwQ8wIwAg#
http://www.bumperspecialties.com/home-en.php
That should get you started.