The producers will restrict teams for safety, security, or other production related reasons. (In the early seasons, especially immediately after 9/11, Athens and Frankfurt had a poor security reputation, for example.) Other restrictions may be due to visa or other requirements specific to a certain country.
As far as I've read over the years, there is not a master list as such, it has to be adjusted for changes reflecting the safety, security, or other production related reasons I mentioned before.