Look for the 8020 Linear Motion systems. I could give you some page numbers for the catalogue, but its in my Jeep at the moment. However, they making polyurethane (?) bearing systems. Basically, one piece of 8020 is connected to a bracket that houses a bearing. The bearing connects to the other piece of 8020 on three sides. Similar to this -
http://www.8020.net/Images/Application-Thumb-106.jpg . We built a forklift in 2005, however, we used rollers (which were not the greatest).