My first suggestion would be to look in the "resource guide".
Here is a link to that guide:
http://www.timberframe.org/resourceguide2.htmlAll timber suppliers who have listed with the guild are in this guide.
Next you can use Internet search engines like
www.woodfinder.com or
www.woodplanet.com With woodfinder you can enter the type of wood you want and it should show you a list of the people who supply it.
With woodplanet you can ask for a quote and this quote will be sent out to all parties who are listed with the site and those who have this type of lumber will respond to you.
Good luck with your search.