Quote Originally Posted by FiragaBreak
You can get it before that. Just go in the Highwind and find a cave near the Junon Harbor. Talk to man and he give you information about how many times you died, battled, or used powerful magic. The first time if he gives you an item it would be a Bolt ring. The second time would be Mirthil. When you get that go to the town that's reactor expoded and look for a house on a pennisula. Go inside and there will be a guy asking for your Mirthil. Give it to him and you get a choice between the upstairs chest or downstairs chest. Choose upstairs. Downstairs would be a Gold Armlet.
It's too late to actually apply the Limit manual by the time you get the Highwind. You can, however, get the Mythril as soon as you get the buggy after the initial Gold Saucer visit, since the buggy can be taken into Costa del Sol and over to the original continent. Of course, you can't do anything with the Mythril until the Rocket Town visit, since the weapons maker won't be at his house until after that sequence. You may get the Mythril, by the way, the first time, rather than a Bolt Ring. The man in the cave will give you an item whenever the last two digits of your total battles fought are the same (for example: 277 battles, 66 battles, etc.). Which item you receive is based on whether the total number of battles is odd or even.

Once you've acquired the Tiny Bronco, you can of course go exchange the Mythril for the Great Gospel manual and teach it to Aeris if you learned the preceding Breaks. Interestingly, this is the only Limit manual that can be acquired multiple times, since you can go back and repeatedly obtain the Mythril necessary for the trade.