Silencers are not legal in the state of Iowa. Currently there are 39 out of 50 states that individuals, trusts and corporations can legally own silencers.
There Are no true silencers or suppressors for paintball markers, only mock ones. You need a firearm suppressor permit in order to get a real suppressor, so companies don't make any. Also A paintball gun signature is fairly quiet.
Suppressors are legal, yes.
Yes, silencers are legal in Nevada (assuming they are correctly registered with the ATF)
The local police can assist you.
No, it is illegal to own or use a paintball silencer without an actuall firearm silencer permit. You can buy mock suppressors, which look like silencers but do no significant effect for sound dampening.
Yes. Must be registered with the Federal BATF, but state legal.
The answer can by yes or no depending on specifics which you don't go into.
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There is no liscencing for paintball guns in the US.
yes. you can ship a paintball gun anywhere.
Paintball is not illegal in Japan. You can play at the related link.