https://www.amazon.com/gp/aw/d/B01DBYWDAQ/ref=mp_s_a_1_13?ie=UTF8&qid=1488582864&sr=8-13&pi=AC_SX236_SY340_QL65&keywords=25mm+plastic+balls I think this would be your best bet. I've seen a post around this sub where the guy used a set with these. I think you may have to drill a hole in them but they should work great.