It looks like Toywiz already has pre-orders available for the series 2 trading cards. The release date is a bit on the odd side though. It's looking like they wont be sending them out until October, even though they technically release in April. The number matches up to the usual pony trading card boxes, so it may just be a typo!
Anyway, find them here! Thanks to SwanDive for the heads up.
Update: Looks like these have been bumped up to April, it was a Derp!