Basically, it's better to play it safe and assume you won't ever get your miracle token back. If you suspect Cultar coming after yours, or you may get executed, consider using it sooner than later.
consolidated overview, only ways appear to be:
1) An Ambitious Operation (admiral chooses)
'-1 fuel. The Admiral chooses another player to gain 1 miracle token.
Roll a die. On a 4 or less, -1 fuel.
raiders + jump
Unless you know your fuel situation is A-OK, it's gonna be a hard sell trading a Fuel for a mt. Ironically enough, if Fuel's doing OK, you probably may not have needed the mt anyways
2) 5 - A Second Chance
Play before cards are added to a skill check. If the check passes the printed difficulty by 4 or more, the current player gains 1 miracle token
3) Use Cultar's special to ferry around miracle tokens
4) Rescue Hera (mission card) 20YPR
Each human player that does not have a miracle token gains 1 miracle token.
-1 morale and destroy a raptor.
There's one mission that gives all human characters who've used their tokens one if you're using the Demetrius/Earth option, and there's one Tactics skill card called "A Second Chance" that will grant the current player a miracle token if the check passes by more than four over the difficulty.Unless I fudged up somewhere on my spreadsheet, this appears to be the only crisis.
There may be more than one crisis, but I don't know.
And that is an important distinction. If Cultar already has 1 or more mt, passing that Mission won't give him another.