I hadn't really considered the gun collectors, but yeah you're right. Personally, I like Chris Rock's idea for gun control. Who says that guns have to be affordable? If the government can tax smokers, why not tax gun owners? There are many more opportunities to tax gun owners as guns require regular maintenance and people buy accessories for them like different scopes, triggers, types of bullets, gun oil, etc. This might not address the guns in circulation currently, but it would certainly cause people looking to buy a gun through legal channels to consider whether or not they can live without owning one.
Its an interesting idea, but the people going out and buying a whole bunch of accessories for their guns aren't the ones that being targeted by the law and most of them right-wing anti-tax as they come so there is an even slimmer chance of anything laws passing. At the end of the day I think somebody is going to have to bit the bullet and push a gun law through and let the results speak for themselves, because I don't think that talking or debating about it more is going to give us a better law.