July 21st: RNC ends
July 23rd: Washington
July 25th: Missouri
August 1st: Arkansas, Kansas, Maine, Maryland, Nebraska, New Jersey, Pennsylvania, Vermont, West Virginia
August 2nd: Massachusetts, Wisconsin (South Dakota has clear sore loser law)
August 10th: Alaska, Colorado, Connecticut, Hawai'i, New Hampshire, Ohio, D.C.
August 12th: California
August 15th: Utah
August 17th: Montana
August 18th: Alabama, Tennessee
August 19th: Iowa, Louisiana
August 23rd: Minnesota, New York
August 24th: Idaho
August 26th: Virginia
August 30th: Oregon, Wyoming
September 5th: North Dakota
September 9th: Arizona, Kentucky, Mississippi, Rhode Island
And he'll get challenged in about 95% of these states because they have sore loser laws (45/50 total states), in which despite existing precedents (mostly by the LaRouche people) apparently don't always mean anything if 2012 was any example.
In order to get on the ballot nationwide, it is estimated that an independent presidential candidate in 2016 would need to collect more than 880,000 signatures. California is expected to require independent candidates to collect 178,039 signatures, more than any other state. Tennessee is expected to require 275 signatures, fewer than any other state.
In some states, a prospective independent presidential candidate can more easily access the ballot by forming a new single-state minor party or affiliating with an existing one. If a candidate were to opt for this hybrid method of ballot access, the total number of required signatures would drop significantly. According to ballot access expert Richard Winger, it is easier for a candidate to run with a new single-state party than as an independent candidate in the following states: Arizona, Delaware, Florida, Hawaii, Maryland, Mississippi, New Mexico, Oklahoma, Texas, and Vermont.