I m not sure if you can buy a Brand new 1Jz 0r a 2JZ , i guess you can check with Toyota Motor corp, Other than that you can get used ones from three places ..
Used japanese market (which is really good cuz less mileage on the engine, but high price)
Sharjah old engine market ( price is right but the engine has loads of miles on it)
Local old engine markets either at karachi or Peshawar.
I have seen a 1JZ swap in a rx8 and it was amazing. you can contact Faizullah (03339122299) in Peshawar he can give you a complete package of the swap, last time i asked he was charging around Rs 280,000/- for the complete package and in this swap every thing is working even the AC (:)) .
Rest 2jZ would be really crazy in a rx8 but seriously it would be FUN .... I have both the engine and the car and one day i will try to make it happen .....
Rest best of luck