I don't have an actual guess, but...

Only two chances do you have to see me - You only visit Midgar twice. I don't recall another area where you are limited to two visits.

The origin of such is found in antiquity - This actually makes me think of the rocket at Rocket Town.

Only to be seen never to be held - Evidently it must be apart of the background or scenery if you cannot hold it.

Do not try to find me iv been expelled - This links with the second line in making me think of the rocket, a part of the rocket even.