ECB 3D Printing has included their Dual Shock Mounts in their NEXT LEVEL Monster Truck Conversion Kits for years, and now you can buy them separately! 
 
These 4 parts mount to the SCX24 axles and allow you to use 2 shocks per axle (assuming you have a place to mount the upper part of the shock already).
 
All printed parts come in black as shown in the pictures.