how do i get 50 htz power locally in the U.S. ?

I would just run it at 60 Hz. Output rpm will be 20% higher.

Alternately, you could get a 400V VFD and set it's output to 50 Hz.

You've got a serious problem. Nowhere in North America will the public grid give you anythng other than 60Hz. There may be some private company running some European-spec power equipment and using their own 50Hz private grid to do it, but finding them will be a problem.

Because of this, your best bet, if you must do the testing yourself because your vendor can't do a demonstration for you of the motor, may be to gernerate the 50Hz yourself. This means acquireing or renting a large generator, or perhaps a motor-generator if you want to run off the grid, which has a 50 Hz output. Or replacing the 60Hz control seciton in an existing generator with a 50Hz one. Not something I'd suggest, likely to be expensive, and perhaps difficult to buy separately. there are probably generators which have adjustable output, but NAmerica is so tied to 60Hz that the market for them is likely to be very small. This is going to be a major issue since you have a rather large motor to test.

Alternatively, I think you should probably resign yourself to finding someone else who is already set up to do such testing. In practice, this is likely to be your best bet. The motor vendor may have some suggestions, your local power company (industrial division) may have some, a local industry using large electrical equipment (eg, motors) may have some (mining, ship building or maintenance, railroads, electrical subway, heavy manufacturing (ie, steel fabrication, stuctural assembly, bulk material handling (concrete, sand, grain, oil pumping, ...). You may be able to 'rent' their internal test facilities, or use the power equipment contractor they use. Or try the motor manufacturer if you're not getting it direct. Even if they're in some other city, the engineers there may have an idea. The marketdroids are rather less likely to.

It will be fun moving the motor to the test setup, or the test equipment to the motor. Hope you've kept up on your forklift license. And your millwright certificate too! Might it not be worth it. Even if the motor is well-priced?

Several tests can be made of such things as bearings, electrical continuity, rotor reluctance, ... which together might be equivalent ot an actual operating test. Could these be substituted?

Good luck.

This is probably a pretty dirty solution, but if you are an electric motor builder or dealer, you may be able to get a larger motor and use it as a generator. The problem you'll have (not so simple, but doable) is to get a way to diliver 200hp with controlable speed to the shaft/axis of that motor. You can adjust the speed (rpm) to generate 50hz.

I've had that problem with motors before, and I've also gotten a VFD (variable frequency drive) to work fine.

If that turns out to be a problem (some non synchronous motors dont like VFDs), then the rotary inverter option is your best bet.

oops, I wont say actuator because I'm not sure if thats what its called. But you cant get 50 hz service in the US, you need a mechanism that changes 60 to 50

Buy your own generator. Some generator can be adjusted to 50 cycles.

I have seen a military surplus generator that has a variable frequency.