Apple began running out of pre-order iPad inventory less than 24 hours after pre-sales first began. Now, it looks like all of Apple’s initial iPad stock has been depleted. The company’s online store currently shows an estimated ship date of March 19th for every available iPad model, including the 16GB, 32GB and 64GB Wi-Fi models and each of the three iPad Wi-Fi + 4G versions for AT&T and Verizon Wireless. Apple unveiled the new iPad this past Wednesday at a press conference in San Francisco. The latest version of the wildly popular tablet features a Retina Display, a dual-core Apple A5X processor, an improved 5-megapixel camera and a slightly redesigned case. Early pre-orders will become available on Friday, March 16th.