Since you want a tyranitar with thunder punch, your only reliable change is from move tutoring him.
Thunder Punch is the physical move - and a pretty strong one. Since this might be too much trouble, you can make it remember a move similar - by paying a heart scale. Thunder Fang is the closest move since it provides the physical part of it - but it has 5 less accuracy and 10 less base power (stinks).
You could've went with thunderbolt/thunder - but it's a good choice you didn't seeing that he's more physical than special.
Instead on electric, you can choose fighting or rock (brick break and stone edge - respectfully). Electric has 2 super and 3 non effective.
Fighting has 5 and 5 effective.
Rock has 4 and 3 effective.
(Suggestions - don't have too take it)
Hope I helped! :)