do you mean the car bounces too much on the track? over/through bumps or off jumps?
30wt with #1's in the rear shouldn't be too far away but I know the Ghea pistons are popular - check
http://www.p-dubracing.co.uk/ for availability.
with #1's you might find that you are bottoming out off jumps and/or big bumps, so increasing the pack (by using a smaller holed piston, such as #2) might help. however, the #2 pistons will not normally go through rough stuff as well as #1 - thats where the Ghea pistons come in.