That would appear to be the case, yes. At least, I don't see that show in the iTunes Store either. Since the show was cancelled back in May and the rights to re-runs now belong to the SyFy Channel, the license to Apple to sell the episodes probably has been pulled by Warner. Sorry, but it appears you're out of luck. Keep backup copies of the episodes you already downloaded. Should you want them on another device, you'll have to copy/sync them there yourself from your computer.