I haven't in a long time, but yeah, I used to repair T21s (er...I just to repair PC juniors, but that's another lifetime ago...
IBM isn't the OEM for the hard drives; they buy them on the open market. It's the form factor you need to get. The actual manufacturer (Maxtor, Seagate, whatever they used) will be on a white label on top of the hard drive. The IBM-specific bits are just the mounting hardware; anywhere from a piece of plastic on the outside, to an actual cage in the later models. If you replace the HD, please just save the mounting hardware (you don't get those if you're ordering from Lenovo, who took over the IBM bits).
As long as you haven't enabled a logon password, you should be fine, but you'll have to load an operating system, etc., to get it back up and running.
For that matter, you might check with a refurbishing center (we used to use Planet ROI in New Jersey, where for some strange reason almost all hardware depots seem to be... to see if they have a T30 (or something even more recent) that works, at an affordable price. The place I worked at was sending palette-loads of T42s, T60s, Dell 620s and 630s off to places like that.