Hiya
The TC uses a standard 3.5" sata drive..
Apple do not sell drives for TC.. nor do they do the upgrade. nor do they repair them or open them.. even when dead they will not help you remove the hdd for file recovery.. in fact Apple will do nothing!! If it is under warranty they replace them.. as per the requirement of the law.
You can basically use any size that was originally available.. generally 2TB are ok.
Nor is the TC particularly bothered by drive brand or other details.
Mostly Apple now use WD green drives.. but sometimes I have found Samsung, Hitachi and WD black drives.
You will gain very little speed using 7200rpm drives.. so green drives are probably good.
Watch the new format type drives though. I tend to recommend to people find out if someone else has had success with a particular model drive.. rather than be on the bleeding edge.
If you want to use 3TB drive these are proving much more problematic in the Gen2 and Gen3. strangely they do seem ok in Gen1.
There is a fair bit of info in forums.
This one is particularly helpful.
http://arstechnica.com/civis/viewtopic.php?f=19&t=1125622