The answer is; no where. However, it's not that simple, you may have noticed that BC Games have disappeared from the games page, their tab no longer exists.
The feature was introduced back in December 2010 and users were very vocal about the new feature. Opinions were mixed, many users without a Builder's Club membership felt they were being left out and features were being taken away from them. However, some users argued that it was simply adding a Builder's Club benefit, and was not actually taking anything away from the NBC experience. The point of the BC Game feature was for people to ultimately join BC, they would see a game they really wanted to play, and buy a premium membership.
John Shedletsky stated that the actual reason the BC Games tab was removed was because the system was heavily exploited by users. You may recall that many popular game owners, created two versions of their places; a BC version and a NBC version. This defeated the purpose of the feature, players would not need to buy BC to play the game they wanted, they would simply visit the NBC version. Meanwhile, place owners were making huge amounts of tickets exploiting the system and so ROBLOX removed the tab. John Shedletsky stated it was a 'failed experiment', but the tab may return.
In short, Builder's Club only games are not gone, you can still play them but you will not find them in the Games page.
Editor of Roblox News