As others have posted, if you want to rent a "standard" stroller that can be done through a number of stroller rental companies. If your son is larger, uncomfortable in a standard baby stroller, and/or you wish to have a special needs stroller - PP indicated the Liberty Pushchair is available through a regular stroller rental company. Or you can contact the medical companies listed in the FAQ sticky. At least a couple of them have the Maclaren Major and/or OttoBock special needs buggy.
Good luck and enjoy your vacation!