Not sure if you're still looking for material for frame rails, but I found a supplier that deals in Metric sizes. I found
www.metricmetals.com and I got my aluminum from them, their website has a really good description of what they sell, and they'll get you a quote within 24 hours Mon-Fri, they'll even cut the 10' stock down to whatever length you want, and they'll ship the drops with your order. They've got thicknesses from 2mm and up on pretty much anything you need.