Two additional sources of parts which may or may not be related to power and trail trucks include Wiseman Model Services operated by Keith Weisman and Micro-Loco-Motion.
The 1st additional source is Wiseman Model Services http://www.locopainter.com/ . Keith Wiseman has been attending O scale meets in the Midwest area for the past decade or more. I've seen him at both the annual March O Scale Meet held in the Chicago area and the Indianapolis O Scale Meet.
Keith started out in O narrow gauge and broadened the scope of his products. He recently added the Back Shop line of O scale brass castings to his product line. The Back Shop had many fine castings applicable to O scale trolleys.
Keith has a wide range of products which can be used on a layout including buildings and vehicles. Check out his web site.
The next additional source is Micro-Loco-Motion http://www.micro-loco-motion.com/ . They were found during a search of the web for can motors.
I've never ordered or have had any conversation with this supplier. However, if you look at the web site they have a wide variety of can motors of various sizes. Furthermore they seem to be are very knowledgeable regarding their products and willing to help you pick the correct motor to meet your needs. Check them out.
I need to look at their web site some more myself. In the meantime back to other projects. We will be back to power trucks with the next post.