Moves that boost rate of hitting that have not been mentioned are
Odor Sleuth/Foresight/Miracle eye (does not technically improve accuracy but returns foes evasivness to normal so still can cause an easier time hitting the foe)
Mind reader/lock on ensures the next move will hit but cannot be learned by excadrill so in your case this is useless
If you really want to improve accuracy for Excadrill I recommend the move hone claws, the item X Accuracy or if excadrill is slow zoom lens will boost accuracy 20% if he is fast wide lens boosts accuracy 10%.