I bought my Flames RBK authentic from this place:
http://sportsk.com
They're based in Detroit and shipping was fast, I had the jersey in Calgary within a couple of days. They were the cheapest I could find anywhere (by far) and the jersey was still in the plastic wrapper from the factory.
It's looks like they have a limited selection of practice jerseys:
http://sportsk.com/repenhlprje.html
http://shop.nhl.com also seems to have them for every team, but they're more expensive. An eBay search probably wouldn't hurt either.