What the US needs is instant runoff (via ranked choice) voting.
Short of that, people with your mindset need to volunteer, fundraise, and vote. Otherwise those parties will never match the scope of the current duopoly.
Instant runoff only really resolves the spoiler effect. I think it's extremely unlikely we'd see a third party come even close, including with instant runoff, to taking power. I'd look at the problem numerically. Imagine a state has 100 representatives sent to congress. And we know this state is let's say 30% republican, 30% democratic, 20% libertarian, 20% green. What would you say their representation should look like? Everybody's going to say the exact same thing: 30 republicans, 30 democrats, 20 libertarians, 20 greens. The only problem is that you only get that distribution with proportional representation, which as a nice side effect also would do away with gerrymandering since you don't need to carve a state up into representative districts anymore.
The downside here is that proportional voting doesn't stand a bat's chance in hell of ever getting enacted because it really would lead to a major upheaval in DC. And the very people that would be 'losing their jobs' are the ones that'd need to work to pass it, which would be a tremendous undertaking. You'd need a 2/3rds majority in both the house and senate to start the process, and then you'd need 38 of the 50 states to ratify the change. And at the end of this process the two major political parties, who are in control of every single major political body in the United States, would have just ceded a tremendous amount of power.
The funny thing is, I see merit in both parties. I like conservatism when it comes to the 1st and 2nd amendment protection, freedom of religion, etc, but I hate how the right treats the environment as a resource to be wasted, used, and abused. I think the libertarian stance on drugs is a little too extreme (I think drugs should be legal, but that they also shouldn't necessarily be easily accessible - people should still have to jump through a few hoops to get them). Rinse and repeat of a lot of issues.
If it were possible to transcend parties and vote just for candidates that represented my nuanced beliefs, I would switch in a heartbeat. Instead I'm forced to prioritize which issues are most important to me, and then plug my nose and vote for the party that best represents just those (even though said party comes with a lot of undesirable baggage).
Have you considered voting Libertarian for federal positions and a mix of Democrats and Republicans for state and local positions (depending on size of city/state and specific concerns)?
Isn't the American president a barometer or descriptive reflection of the democratic population? Or does one define American conservatism by reciting a prescription of what people ought be when they say they're conservative?
Similarly I presume the rise of Boris Johnson with Brexit is a reflection of the British people, regardless of whether he has his conservative credentials in order.
What the US needs is instant runoff (via ranked choice) voting.
Short of that, people with your mindset need to volunteer, fundraise, and vote. Otherwise those parties will never match the scope of the current duopoly.