I am not sure if it can be repaired... since i can't see it, some of the older model thinkpads like you have it could be done however it sounds like the actual plastic mounting bits have broken off? ( that hold the key to the spring type thing which is in turn attached to the keyboard frame etc).
The easiest thing to do might be to get a nice used keyboard on ebay for it, since the keyboards are so easy to replace ( compared to other model laptops)...... this might be the most cost effective repair since it would not be expensive and would involve the least amount of time ( taking the entire keyboard apart and trying to replace the little plastic parts that would be hard to get)...... there should be a model number on the keyboard once removed so you can make sure you find the correct one..... or the powersellers are usually helpful if you ask them if a specific item will work for you....include your machine type ID for your thinkpad etc.
You might be able to find the key along with the plastic spring parts on ebay however that would require complete teardown of the keyboard it's self. = taking the keyboard out and about 20 screws with a layer and maybe some glue... it's been awhile since i worked on this model, if it was newer it might be worth trying to take the keyboard apart.