The HEMI I suspect you can find aftermarket Camshafts.
The 4.7L, I doubt you can find them, and the 3.7L I doubt even more they exist. If you look at the chain drive for 4.7L and 3.7L, I personally do NOT think messing with that is worth the few extra HP that an aftermarket cams may provide. Definitely NOT worth it for the sound.
Changing a Camshaft is a lot of work, since you have to ask, its fair to assume you'd be paying someone to do this and that will be a hefty bill, especially for the 4.7L and 3.7L. Seems an awful lot, if you're just interested in the sound.
The Camshafts control the opening and closing of the valves, and thus control the characteristics of the air flow through the engine. Changing the characteristic of the airflow through the engine (and more goes into that than just the CAMS) will change the power and torque, NOT just the peak, but the curve for those. That is why they change the sound of the exhaust, and they also change the mileage, the smoothness and the idle of the engine.
And they also change the pollution output of the engine. So unless the Cam you buy says its CARB Exempt, which also means it won't be that much different than the stock cam, it will increase the pollution output. Thus, arguably that makes it illegal if you're going to drive on public roads. (Lets avoid the EPA/State Law arguments, I likely agree with you). Honestly, the only way you'd get caught is through pollution inspection and then you would have to return to the original cam, a lot of work/money. Remember, Commanders are OBDII compliant, meaning they monitor and test themselves for pollution compliance, so if the cam you choose is radical enough, it will cause Check Engine Lights.
And that is probably the biggest reason why you don't see many aftermarket cams. To market a Cam that is "legal" and passes pollution inspection, it likely will only give you only a couple of extra HP, hardly worth the effort and cost of swapping cams, especially when you have other alternatives that can provide more power.
Of course, for a lot less you can get an aftermarket muffler or exhaust system that will give a sound similar to what you seek. As well, you can get tuner devices that will provide extra power with a few minutes to hook up the device to the OBDII port, and if you fail pollution inspection, you can just hook up the tuner device and return it to the stock tune.