In NJ up until 1997, no third party candidate for governor had ever gained over 5% of the general election vote. So the Democrats and Republicans, several generations ago, created laws requiring third party candidates to get over 5% in the prior general election to get an automatic line on each county ballot for the next election. This law in effect blocking third party candidates was further strengthened 5 times, as recently as last year (regarding matching funds laws), in an attempt to make sure no third party candidate for governor ever attempts to shake up the corrupt duopoly in the state.
This country does have very serious barriers to entry for all third party candidates. Paul had to run that gauntlet, the beatings from the bureaucracies leave permanent scars.
I don't know about NJ, I presume Ron Paul would leave that decision to the states.
California had around 130 candidates in their last Governors race, their choice too.
The Florida butterfly ballot above has 11 candidates. The Libertarians were on 48 ballots last time round, Reform and Constitution about 3 dozen states, Green a couple dozen, six parties on 2/3 of the states in 2000, so Paul's complaint isn't that he can't get on the ballot as a "third party", the fact is he's really talking about 6th or 7th or in Florida 11th party run.