These are Hot Swappable SCSI Drives and as far as I'm aware the biggest that are available is somewhere around the 146 GIG Capacity and they are expensive really expensive.
Anyway Seagate Make HDD's that will suit this computer so all you need do is look up what is available from Seagate and then check who sells them in your area. But knowing these drives and how much they actually cost they will most likely be Special Order and whoever you approach will want a serious Deposit before they consider ordering them. The current largest that I use in the Barracuda Range is 50 GIG and that was all I could afford.
Here is Seagate's Technical Information on the drive that you are looking for and they are currently available in up to 300 GIG Sizes but I haven't seen any prices for anything bigger than the 146 GIG Capacity.
http://tinyurl.com/29drm9
Here is the Seagate Sales Locator
http://tinyurl.com/22m3qb
What you are looking for is the Cheetah? 15.5K Hard Drives range which now come in sizes from 73 GIG to 300 GIG Capacities.
Col