They drop later on in event maps... but rare (like ampys). Just get what you can, save up for skill blooms (for now - they are also used for something else much later) and don't fret so much about them.

BTW: skill triggering makes a HUGE difference, you can easily wipe out everything non-boss without taking any damage. So much so, that the units that boost skill rate activations are often some of the most sought after (and they work as a multiplier on your base rates, making skill level highly important as well).

I think its only use for buy Lotus, for increase skills of 6* or double 5*