It has probably been discontinued since it used the older 33GB platters. WD has moved on to using 40GB, 60GB?, 80GB, and even 83GB platters. Chances are that the 40GB units will be switched over to the 80GB platters soon. Less parts to manufacture.
Edit: On PriceWatch there was only 1 vendor that had it listed. You can most likely find the 120 GB version for around the same price.