This is actually fairly easy, if you have access to the right Pokemon. The right Pokemon in this case is Xatu.
Xatu is in the Flying egg group, the same as Sigilyph, so they can directly breed with each other.
What you need is a male Xatu, which knows the moves Stored Power and Psycho Shift. They learn both these moves levelling up, at levels 47 and 37, respectively. Now breed that male Xatu with your female Sigilyph. All of the offspring will be Sigilyphs that know Stored Power and Psycho Shift.
The downside to this method is that I am pretty sure that Xatu are only found in the Friend Safari, so if you don't have a friend with Xatu in their safari you might be out of luck. But try the GTS or have a look around for someone with Xatu in their safari.