Yes, the "Invector - Plus" Chokes are your ticket. These choke tubes are 12 Gauge only for current and past Winchester shotguns: Model 101, Supreme, Select, SX2, SX3 and SXP shotguns.

Hi Shane, They come with Invector plus chokes Includes: Three Invector Plus Flush Chokes - Full, Modified, and Improved Cylinder

Yes the SX3 takes browning invector plus chokes

Hi Shane, They come with Invector plus chokes The Winchester SX3 Waterfowl Hunter is one of the best auto loading shotguns available today ready to take on the worst conditions mother nature can throw at it! Its comfortable ergonomics, sleek profile, and rugged reliability are available to you at a price you can afford. Precision manufactured and engineered for endurance the Super X3 will continue to excel in even the most abusive weather. Featuring a 28" chrome-plated barrel, a Tru-Glo fiber optic front sight, and Active Valve gas system, the SX3 provides exceptional accuracy. The Active Valve gas operating system automatically adjusts to allow the exact gas pressure necessary to fire a wide range of loads, giving you a greater versatility in the field. With an adjustable length of pull, the SX3 can be suited to fit nearly any shooter. An Inflex Technology recoil pad minimizes felt recoil, making the SX3 a comfortable pleasure to shoot all day long. Lighting-fast operation, lightweight design, and proven reliability, makes the Winchester SX3 Waterfowl Hunter a great choice for the serious bird hunter.
Includes:
Three Invector Plus Flush Chokes - Full, Modified, and Improved Cylinder

Yes the Invectors will fit the SX3