If you are talking about the long sleeve , female Foster QC fittings, check AliExpress. They are available with different whip fittings. Then there is another potential issue with their use. That is the sliding feed sleeve diameter. They are slightly larger than the stock openings on FX rifles and will interfere to the point that they do not always lock in place over the male foster on the gun. That leads into a rather explosive surprise. The remedy is to very carefully trim the wood about the gun fitting. The action must be removed from the stock first.