Wallmart here doesn't sell things like this, just motor oil in the best case scenario, most cars here have manual transmission. However, Dex III is usually available in parts stores in 1 liter bottles (about a quart) for the price you pay for a gallon in the USA, lol (still cheaper trying this than rebuilding the transmission!)
I looked for Trans-X on the auto parts websites here and couldn't find it, I also don't know nothing similar... maybe I could ask in a transmission shop.
No, I bought the jeep with this prolem (thought it was easy to solve

) and then I took it to the shop to change the fluid and clean the valve body... the old fluid was dark brown (the best one I've seen in the XJs I looked before buying this... I think people are affraid of changing the tranny fluid)