I don't think that free servo samples exist, as servo is a finished product in its own right rather than primitive component.
Also, to make servo costs much more compared to cost of production of primitive components, hence I don't really think that anyone would give them away free of charge, at least not for hobbyists, maybe for businesses that are potential costumers for big amounts.
Moreover, there is not really much to be sampled as all servos work in very similar way, only characteristics are different which are well represented in datasheets. If for specific application there is a need to have servo capable of xxxx torque and yyyyyy angular velocity, that means You simply buy servo with required specs.
