I made one, piece of cake. "Borrowed" a big glass syringe from work which had a fitting on the end normally designed shockingly enough for a needle, i then found some clear plastic tubing the correct diameter to go over the stans valve (core removed of course) and heated it up/semi melted it onto the syringe at t'other end.
Works great! No leaks and cost me all of 50p to do.