Hi Mate
Tyga do a race tail for mc18 useing stock subframe here http://tyga-performance.com/site/product_info.php?cPath=72_78_101&products_id=482
They have exast to here http://tyga-performance.com/site/product_info.php?cPath=72_78_100&products_id=545
contact them for both .
Or the other option is a set of second hand chambers from japanauctions here is one set http://www.japanauctioncenter.com/view2.php?seturl=http://page7.auctions.yahoo.co.jp/jp/auction/g81617363 and a cheaper set http://www.japanauctioncenter.com/view2.php?seturl=http://page17.auctions.yahoo.co.jp/jp/auction/v130733190