I was going to post a guide to identifying Blind Bag Pony packages, but Kittenshy over at Deviant Art has already knocked that one out of the ballpark! All I can really add to it is that the identifying number you’re looking for is on the back of the foil package, stamped into center strip. It’ll be a backwards number that’s a bit awkward to read! That number will correspond to the ponies in Kittenshy’s pic.
And if you still want the whole box in one go, Hasbro Toy Shop has them in stock! You have roughly 20 minutes until they’re sold out all over again!