All Alfa Romeos are hard to find in the USA. A 164 Q4, to make matters worse, is one of those special edition Alfas where even fewer of them made their way over here. Also, even as brilliant as they are in difficult to explain ways, Alfas aren't very reliable. So with the ignorant, impatient, and infantile "when it breaks throw it away and buy a new one" attitude that has become so sickeningly common here in America, more of them have been junked than I even want to think about.
It's entirely possible that you will find one, but it might take a long time, and the price might be a little higher than you would expect.
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"Ok, systems check; the battery is discharging, the oil temperature is very high, the oil pressure is very low, the engine temperature is off the end of the scale, I'm running out of petrol... but the clock is correct!"
-James May, in an old, worn out Lamborghini purchased for less than £10,000.