With few exceptions, any factory-equipped electronic option can be added after the fact to any car...if you want to spend the money. Generally, you'll be dismayed to learn how many parts you really have to replace. A lot of times, you learn that by the time you buy the parts, control modules, switches, trim pieces, and everything else that's different in cars that have the option, the cost becomes prohibitive.
For something as tightly integrated as adaptive cruise control, I wouldn't be surprised to learn that the cost of retrofitting it is more than the cost of trading in on a new model with the option you want.