I know I'm twisting the meaning of the question with this, but if you take the Triforce as referring to the complete Triforce (all three pieces combined), then that could be implying the existing three Triforces as being the Hyrulean Triforce, the Lorulean Triforce, and the Terminian Triforce (although it hasn't been confirmed to exist, it was hinted at in a few places)... in which case I'd place a hypothetical fourth Triforce as existing within the Twilight Realm.
I also have a theory that Din, Nayru and Farore would have created all of the Triforces... so all of them represent power, wisdom and courage, albeit in different ways... e.g. the Hyrulean Triforces represent possession of those traits, while the Lorulean Triforces represent overcoming a lack of those traits (Ravio was a coward, but travelled to Hyrule in search of help... Hilda had repeatedly acted unwisely, but eventually realised the error of her ways... and Yuga's own power was relatively weak, so used the power of others instead... and it's only after all of this that their Triforce is restored).