Your cabinet company would be the first place you should be shopping.

Barker cabinets sells them unfinished in all the types of wood they build cabinets in.

I think they are under millwork. If you want them unfinished though it seems like it would be pretty easy to buy the lumber and build them, they are pretty straightforward.

Thanks for the suggestions, but the light rails from my cabinet maker and Barker's millwork are just too blaahh and either too narrow or too wide. I'm hoping to find a company that makes them with a little style. Too much work is going into the project to stick a squared off piece of trim under the cabinet and call it a light rail.

Nice.

We used a triple-bead molding we got from Raw Doors for a light rail. They have some other light rail moldings also and carry a variety of woods. We placed 2 orders with them and the material was delivered promptly and packaged well.

Here is a link that might be useful: Raw Doors

I appreciate the suggestions. It looks like I'm going to have to customize a standard molding to my specs. I'm going to experiment on a sample, but here's what I'm planning (check the link below)
The cabinets are frameless, modified shaker, so I'm planning on rabbetting out a 1/2" x 1-1/4" section from the back of the molding and using it vertically.
Never a dull moment.

Here is a link that might be useful: moulding info