I doubt you could get one prior to arriving.
When you do arrive you walk into a large Orange or Cellcom or Pelephone store and say you have an iPad and would like a data microsim. They should know what to do from that point on.
Cellcom for certain allows you to get one with zero obligations, so you can terminate your contract at any point no questions asked. I believe Pelephone does too, not sure about Orange.
Ask them. They'll help.