There aren't any specifically made for the SIM-4, but I'm sure there is something out there that you could use. I recommend using a remote coil setup because it'll act as an expansion chamber and you won't have to have your tank attached to your marker. Hope this helps!
I need to correct myself here...you CAN'T put an expansion chamber on the SIM-4 because the hand guard would get in the way. You would have to settle for a gas-through fore grip for gas expansion. I still recommend using a remote coil.