Why would anyone buy a car that you can't get into gear? Tell the seller to fix it and then it can be test driven. Did you read the answer above? There is no cable.
The most likely scenario is that the trans is shot and someone is trying to hide that fact by claiming it is a "minor" problem with the linkage.
The linkage is attached to the steering column as it protrudes into the engine bay, well one rod this goes down to a linkage mounted on the drivers side frame rail, then another rod to the transmission shift selector on the drivers side of the trans, you can see it if you look under the car far enough.