Like puffon said, the vape mail ban via USPS is not yet in effect. However, it may be that the particular vendor you’re used to buying from decided to stop selling eliquids online and shipping them. That’s what quite a few vendors did as of about the end of March.
But…there may be other vendors who ARE still selling online and shipping product…who DO have your preferred eliquid! If it is a well-known and/or popular eliquid, IIWY I’d do a Google search to find those vendors.