If you don’t have such a centre (I’m looking at you Canada) you’re not likely to be competitive with the top nations.
In the glory days of the former Soviet Union (and the new Russia) the centre is Round Lake.
Some athletes live there year round, some come to “camps” on a regular basis.
Brigid discovered a book called The Russian Heart: Days of Crisis and Hope (1992).
It includes some interesting content concerning Round Lake, back in the day:
… While the training is completely professional and disciplined, the facility is rudimentary and the dormitory conditions sparse. Though the food is much better that that available to the general public, it is, by Western standards, very basic. …
details on Couch Gymnast – Soviet Gymnastics: Days of Crisis and Hope