Anyone can sell a vuln in any jurisdiction and never be caught. Lets not pretend the law is actually worth a damn here.

We need an anonymous bounty system.

Are you claiming that if I sell 0day through a broker to the national Government of a given jurisdictions that the national Government of that jurisdiction is going to criminally penalize me?

If so, that's a bit naive. In the actual world, that buyer wants to buy more stuff from me, not penalize me.