How to get designs for orange gear

How can I get designs for the orange equipment?

There is no easy free way. When you keep killing higher level beasts grade 5 design fragments can drop, which can result in orange designs when you synthesize them. For the rest it is a matter of keeping your eyes open to get orange design fragments from special events etc. Before forking out a lot of gold (or money) to purchase an orange design be aware that it also costs a lot to craft (material and steel cost).