We've been experiencing an issue with the way the store is handling the Lancer Paragon and Lancer Rogue Blitzcrank skins. We removed them from the store shortly after their release when we found the bug and have been working on a solution since. We think we've found the cause of the bug, but it will take time to implement and so the skins won't be available to purchase in the store until Patch 7.24 at the earliest.
If you purchased the skin before they were removed you're unaffected. The bug is with the store and is nothing game related.
Sorry about the inconvenience!