Melissa,
Looks like Ruger has stopped making the 7x57 except in their No.1 single shot rifles.
I believe CZ's are still being chambered to 7mm Mauser though. You might also find
an NIB (new in box) or good used one on one of the gun auction websites. I'm listing some links below. Good luck.
7x57, an excellent cartridge. Also listing a link for additional ammo source.
Links:
GunsAmerica: www.gunsamerica.com
GunBroker.com: http://www.gunbroker.com
Auction Arms: http://www.auctionarms.com
Ammo: http://www.cpcartridge.com/index.htm

Edit: Found a couple, but used. One Winchester Featherweight, and one Ruger77.
I'm posting links again. Unless you're in a hurry, take your time. New (NIBs) pop up all the time.
Links:
http://www.gunbroker.com/Auction/Vie...?Item=27692793

http://www.auctionarms.com/search/di...temnum=6367503