The suitcases with so much use it is normal to wear the wheels or some other component like handle or mechanism.
Repair yourself the suitcase. To put the spare wheels normally they are screwed or riveted. In the first case there is no problem, but if the wheels of the suitcase are riveted, you must remove the rivet with a drill or something similar and then screw back the component with screws.
In the case of the replacements of handles or mechanisms, they are normally bolted. In the following link you can buy spare parts of wheels, handles, mechanisms for your travel bag.