vote Donald trump!?

[Thumpalumpacus]

Third-party candidates are not even on the ballot in every state, so there's no way they can when.

Gary Johnson is on the ballot in all fifty states. Hopefully the Greens can use the exposure they're getting this election cycle with Jill Stein -- coupled with the tepid support Hillary is getting from many Dems -- to get there as well. We need alternatives to the two parties today, and I don't care much if they aren't in line with my own views. To me, it's more important to break the binary stranglehold than it is for me to get my particular way.

Ballot access is obviously a key weakness in American democracy which needs to be addressed, you're right; they should not be so restrictive, and they certainly should not (in the case of federal elections) be left to the states to define. One reason why I am registered as a Libertarian is because I want that party to be represented on the ballot even if I don't vote for their candidate. Many states require minimum registration numbers for ballot access, or require a petition with sufficient signatures, in order to place a candidate on the ballot.

What that means is that getting the word out about your candidate so that the various state ballot requirements may be met is the way forward. Such requires a grass-roots effort. But it can be and has been done.

I  think what may end up happening is, since victory for the presidency requires more than a simple majority. so if neither Trump nor Clinton make enough votes it will be possible for something else to happen. What that something else might be, I couldn't tell you.

No, a simple majority is not required. A plurality suffices -- either candidate can win with less than 50% of the vote so long as they have more votes than their opponents.