The only way you may be able to get them is if you have a recent backup that contains those messages. If so, you can connect the iPad to iTunes and then, after right-clicking on the iPad line (under devices) select "restore from backup." Do note that doing this will make the iPad just like the backup, so anything you've done on the iPad since the backup will be gone.
Other than that, there is no way to recover deleted information. The iPad has no "Recycle Bin" or Trash. So, once something is deleted, it's pretty much gone forever. Sorry.
Marilyn