Here's the link to MRRC's website.
http://www.mrrc.com/I have purchased items (cars, chassis, etc.) from them directly in the past and they are very good to do business with.
Also, check out the new Porsche and the new adjustable Monza chassis (looks pretty nice at first glance; way ahead of the Sebring chassis).
Good luck. If you can't find the clear parts that you are looking for, I would email MRRC directly and enquire about them. There's a chance that they will send them to you as a special order; that's the kind of people who run MRRC.
Allan