Since I've never been able to see a stock one, are the aftermarket ones much better than stock?
you can get the BOSS 302 Strut Brace on sale for $100 at CJ Pony Parts.... you will not find it cheaper and it is genuine Ford part.
I installed that brace on my Pony Package V6 and looks like it came with the car, real nice piece. I looked at Ford Racing and Steeda as well, but even at full price, the BOSS brace was still cheaper.
Canadian 2012 V6, MT, Perf.White Pony Package (3.31 gears). Koni Sport Shocks & Struts. Steeda Sport Springs w/HD Mounts, Route 66 SpeedShop 55D rear spring kit. Boss 302 Strut Tower Brace. BMR Adj PHB. BFG G-Force Sport Comp2. Pioneer TS-D6802R Front SPeakers, Clarion 80W/Ch Amp. JL Audio 8 Inch Sub And 175W Amp. GT500 Steering Wheel. 2012+ Tilting Headrests