As title where can buy one

One on ebay here.

2.5 inch Round Rolled Out Exhaust Tailpipe Trim Tip | eBay

Sorry missed the 90 degree bit.

[Edited on 2/2/12 by Gary 7]

Hi
We just used a 90 degree stainless steel elbow , then fitted a straight rolled in chrome tail pipe trim to that
Both available on eBay.
(see my photo archive)
Good luck

[Edited on 4/2/12 by renetom]