As far as I know, No you cant, you have to get it shipped. I bought mine from LEX51S 2nd-hand (the same one u see above in the photos).
In terms of power increases, the IS200 stock exhaust is already a wide-ish one (6cm diameter) all the way through from extractors to the catback. The hi power silent is a little bit wider. And its only a catback only at the end of the day (not a compelete exhaust), so the power increases are only minimal and only at high revs. It will make more difference if the extractors were changed also.
In terms of looks and sound, its brilliant, I love it. Its just a quiet deep hum. Gives the car a sporty look while maintaining the Lexus image ... (will in my imagination it does lol)