It shouldn't even be a big issue to have a special vendor sell them. Just have them be from Johto and they craft them then sell them for high prices due to being very rare outside of Johto. Like maybe 5,000 a piece.
It was such a tease that the special Pokeball store in Lumiose had all of the apricorn balls on display, but did not let you buy them.
If they return this time, I'd also like it if they got actual animations with them. Right now they just share the Pokeball animation.