They are limited editions. The funny thing is that they’re a tie in for Indiana Jones in the US, but overseas (in Asia) they released them as a summer limited edition (with no marketing tie in).
I’m wondering if they’ll come back as a seasonal item perhaps. The Dark Chocolate M&Ms;started as a marketing tie in for the Star Wars movie ... so you never know.
It also never hurts to send a note to the company to let them know that you want to continue buying them.