We have a count of Third-Party Presidential candidates who are on the ballot in a significant number of states. We see:
Chase Oliver is on the ballot in 47 states.
Jill Stein is on the ballot in 38 states.
Robert Kennedy is on the ballot in 31 states, after withdrawing and being removed from some ballots <– correction courtesy Porcus Agricola.
Claudia De la Cruz is on the ballot in 19 states.
Cornel West is on the ballot in 15 States.
Randall Terry is on the ballot in 12 states. However his Constitution Party is running a different candidate, Joel Skousen, in 3 states, so the Constitution party is on in 15 states.
If you look at multiparty Presidential polling, you will generally find Oliver, Stein, West, and sometimes Kennedy. De la Cruz is skipped, even though she is on the ballot in significantly more states than West.
On a related anti-third-party topic, the Democrats have started running ads attacking the Green Party candidate, Jill Stein.
Self correction: on the ballot in 31 states before not after… The rest of what I submitted is correct, as far as I see – thus Kennedy prior to the withdrawals had 49 plus DC,
Kennedy is on the ballots after, not before, withdrawal from additional state ballots. The only state where he failed to secure ballot access at all was New York, where he failed in his legal efforts to overturn what otherwise would have been a successful ballot access drive being disqualified because he used a New York residence address for himself, which is also his long time official residence for the purpose of voting, and the court found that it is not his true residence as he is rarely actually there.
Terry is on in 11 states as a Constitution Party candidate, plus on the ballot in Idaho as an independent candidate. The constitution party of Idaho, along with those of Utah, Nevada and Wyoming, is putting forth Skousen, who is thus on four state ballots. Your combined count of 15 for the Constitutionalists is correct, but both are on in Idaho, Skousen as the Constitution candidate and Terry as an independent.