I think it is only available directly trough Western Digital's web store.
Now for those of you who are tech wizard, I found on their website another external hard drive the My Book Premium ES Edition. That one has the same capacity, 500G, but on top of the usual USB port has the esata port and includes the sata cable.
This product is more available everywhere, so it is easier to find a better price for it (both the DVR Expander and this Premium ES edition have a list price of 199$ on WD site). Also, It can be use for a computer if I decide to stop using it for the DVR.
Can anyone confirm to me that both would work exactly the same for my DVR and I don't need to get the DVR Expander if I can find the ES unit for less...
JR, I would be hesitant in purchasing the second drive. The reason is this unit has specialized power-saving features that *might* interfere with the 8300. You would only know for certain if you tested it. As a few people have found out the enclosure it the critical part. The Vantec's have been reliable for most people.
Not sure if the OP has seen the following thread, however, you can purchase the drive and enclosure assembled (WD500/Vantec combination for example - see the last few pages of that thread) from some stores, and then the startup procedure is pretty simple as outlined there...
As noted by 57, a lot cheaper to build your own but that's another thread.
Videotron has been selling a Maxtor drive for years for use with the SA8300. Have you priced their unit? I see no reason why this shouldn't work but Videotron may specifically prevent it through firmware.