I ordered a Circle F pipe from AMS Racing a couple of years ago. It was available ex stock - they have quite a range available on their current web site as we speak. Price was around $US 150 + postage. The pipe has to be cut to fit US Post's maximum parcel length. I got replica guards, filters, Badges as well for my VR Montesa, cost me from memory $US45, landed at home in 6 days. Not too loud, same top end as the standard pipe, but better midrange. AMS were great to do business with. They have a listing for TM & RM Suzuki models.
Mike