Nuclear Fusion Fuels I have seen some possible fuels for nuclear fusion.
My questions are:


*

*Are there other fuels available even theoretically or the list of candidates is limited?

*What are the requirements that a "substance" should meet in order to be able to be used as fuel for nuclear fusion?
 A: As the content of the wiki page shared by you already states, 
"Tritium is a natural isotope of hydrogen, but because it has a short half-life of 12.32 years, it is hard to find, store, produce, and is expensive. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium".
So yes, the fuel do exist, but some are hard to find while others are produced by certain nuclear. 
Any fuel beside that of the link you provided, yes, theoretically it's possible, but I'm not aware if we have really proved any of it practically though experiments, because of the conditions involving. Just like elements of higher mass fuse inside sun during stellar death.
http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html
http://sciencelearn.org.nz/Contexts/Just-Elemental/Science-Ideas-and-Concepts/How-elements-are-formed
So, we can say it's theoretically available and that's how matter is formed in distant galaxies, but when it comes to experiments, the condition involved are quite extreme and out of our reach to manifest or replicate.
The basic requirement of nuclear fuel is the ability of the nucleus to combine with that of another at very high temperature to form  stabilized nucleus liberating very high amount of energy in form of heat. So the amount of energy that  could be harnessed, how economic is the process, and the availability of the fuel, along with the stability of the output nucleus are some of the basic factors that are kept in consideration while choosing a fusion fuel. There are other factors also, like neutron scattering, radiation(alpha particles) and energy density that comes into play while choosing a fuel.
