Your best bet is to do a search within this forum using "sway bars", "anti-sway bars", "Eibach sway bars", etc. However, since we're a friendly bunch, here is my 2 cents.
My PT also didn't come with a rear anti-sway bar. The addition of the rear anti-sway bar dramatically improves handling performance. The car is much flatter in corners and is easier to control. It feels more solid and takes less effort to drive briskly on a curvey road.
There are several brands to choose from including Mopar. You'll need to purchase a hardward installation kit either from your Mopar parts department (lots if individual parts already posted on this forum) or from Eibach (kit #2860.320HKR) in addition to the anti-sway bar. I strongly recommend that you use the same brand for the front and rear bars. Handling is better matched front to rear for a balanced ride. FYI, Mopar is supposed to be releasing a Stage 1 suspension upgrade kit which includes anti-sway bars. You might check into that also.
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 [IMG]|2003 PT GT 5-Speed | Mopar Stage 1 | Mopar 2.5\" Dual Exhaust | Mopar Short-Throw Shifter | Mopar HO Plastic Intake | Mopar Boost Gauge | AGP WGA/BOP | APC Carbon Fiber Taillights | Axis 19x8 Wheels/Yokohama 225/35ZR19 Parada Spec2 Tires | BTG Strut Tower Brace | BTG Billet Shorty Antenna | Eibach Anti-Sway Bars | HKS SSQV BOV | JLM Motor/Tranny Mounts | KW Variant 1 Coilovers | Maxxfab 3\" Downpipe | NGK Iridiums | Prototypepower UCP/CAI v5 | PTeazer Smoothie Roll Pan | Screamin\' Demon Coil/Livewires | StopTech Slotted Rotors/Hawk HPS Pads/Stainless Steel Lines | Unorthodox Racing Underdrive Pulley|
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