They make different thickness of sabots, try the HPH 24 from MMP and the Crush rib from Harvestor.There are thiner ones and you did not give a gun brand or bore size some companies have a large tolorance on bore dia. some are made to use what they sell.Since I don't have a bore size I am guessing but what you have sounds like one of mine.
http://www.mmpsabots.com/
http://www.harvesterbullets.com/
Lee