LiveScience.com – If you don’t have your iPad yet, get in line.A new seat-of-the-pantssurvey by the research firm Piper Jaffray finds that Apple’s popular tablet computer is in short supply. The analysts called 50 Applestores and found a “very limited” supply of iPads, Fortune magazine’s web site reports. Specifically: 37 stores were sold out. 13 stories had only Wi-Fi models. All 50 stores were out of the 3G model.