It is very difficult to buy a service contract when you are out of factory warranty and have not purchase it at the time of sale.
Some dealers will do it after a full inspection (something you might have to pay for) and you would have to fix anything currently wrong with the vehicle.
Also is your car lowered or have rims that are not factory issued?
If either do not plan on having any suspension parts covered.
A 6 year old vehicle will be expensive to get coverage, but it is definitely available.
If you have any more questions let me know. I have been in the service contract business long enough to answer pretty much any question.