I don't have good news for you. I'm quite sure CZ no longer makes the 550 rifle in 7x57 caliber, regardless of model. Take a look at CZ-USA website: http://cz-usa.com/
The parent company in the Czech Republic has a new website (www.czub.cz
) that is not fully operational yet. It is not yet possible to see the list of calibers for each model. But I remember that their old site didn't list any 7x57 earlier this year. I know, because I've been looking for one too. They listed the 8x57, 6.5x55 and 9.3x62, if you like the metric calibers. Unless I'm wrong, you'll have to search on the used market if you really want a 7x57.
I can't understand why they discontinued it though. Very nice light caliber in my opinion. Sales were probably too low. Good luck with your search !