The best bet for easy "conversion" would be the "Sidewinder Venom" kit from Adaptive Tactical (when it becomes available).
They make the kits for the Mossi 590, but the dimensions are different on the 590 Shockwave and the regular 590 version cannot be modified to fit the Shockwave.
However, the folks at Adaptive Tactical tell me that due to customer demand, the kits are currently in development for the Shockwave.
Although I love the Sidewinder Venom kit, personally I would simply buy an already factory configured mag-fed Shockwave if I was in the market for one.
My preference is to keep my Shockwave tube-fed and go to the Remington Tac-14 (with arm brace and pistol grip) for a mag-fed pump gun due to the improved ergonomics with firing-hand manipulation of the safety.

Aaron, (not worth it in my opinion) two totally different configurations as you know. and requires extensive work to convert. Conversion details video here (Video 1 leads to Video 2 to Video 3 etc) : youtube.com/watch?v=kpPiedHoSfw

Aaron, If you want a magazine fed firearm buy a magazine fed firearm. You can bubba up a Shockwave, but your asking for dependability issues.