I don't know how to get it yet, if you can, but I don't think its possible to accuire a wish tag 'that is usable' because when the girl mentions the wish tag it is not in CAPS like all items. The fact is, i have 6 wish tags. It took me 3 months but i finally figured out what it is, and how to get it. I have found a definition of Jirachi that explains it all. Nobody has mentioned this but.... here it goes....
A legend states that JIRACHI will make true any wish that is written on notes attached to its head when it awakens. If this POK?MON senses danger, it will fight without awakening.
Definition of Jirachi, which i have 2 of, which means that since they both have 3 tags on their heads, thats 6 WISH TAGS, I hope this clears up any confusion. What i want to know now is, how did that girl by the white rock get a WISH TAG? Does she have a Jirachi? Is it the same Jirachi that is suppost to attack you before you go in space after the countdown of launches gets up to 100 or 83, i have seen numerous websites with some stating that launches go bad at 83 and everybody is wishing for the space crew not to die, i have also heard that once the launches reaches 100 the captain invites you to come into space were 'an experiment has escaped' * DEOXYS* and you must catch it..... which is true? Maybe neither? Maybe both? Maybe you battle Jirachi at the rock where everybody wishes, then go up into space where there has been an accident * caused by DEOXYS * and you must use Jirachi to capture the DEOXYS and save the space station.... my launches are at 56 ( i got 241 hours just incase anyone wants to figure out how the launches are calculated to go up ) so i have quite a while untill i figure out if the 83, and or 100, is true. I hope this has helped out a lot and cleared up all of the confusion.