How do you get a thunder stone and when does Electrike learn his first..

The Thunderstone should be in New Mauville by the generator.

You can also get a Yellow Shard to the Shard Hunter near Mossdeep City.

Wow, I thought I would know these right away but, these took some thought.But, I have found the answers.

You get a Thunder stone by Diving near Mossdeep and you should find a Yellow shard somewhere.When you find one, go to Mossdeep and Surf West.You should come across a house, go in and give the guy your Yellow shard.

He will offer to trade you a Thunder stone for it.

You will probably say yes then, you will have a Thunder stone for your Pikachu.

And, considering you didn't know how to get a Thunder stone, you may not know where to get a,Fire stone,Water stone and, a Grass stone.

Well, here is a list of what shards to find and give to the guy.

Red shard:Fire stone
Blue shard:Water stone
Green shard:Grass stone

Now, for your second question.I don't know for sure what level but, it is between levels 0-20.I know the move is of course, it's Thunder Wave.

I don't know why my Electrike knew that move, I hate Thunder Wave.

Hope I helped^_^

You would need to walk/fly to the move maniac in Fallarbor town and give him a Heart Scale which you can get if you can catch a luvdisc which you can find in sootopolis which you will learn about in due course.

Hope this helped!