I found serial number but don't know how to find owner

If it's unlocked go to Settings>Mail,Contacts,Calendars. Under Accounts are listed the owner's email address(s). You should be able to contact them by sending an email to that address. If that doesn't work, try contacting Apple Support. If it's registered, they may be able to contact the owner. If none of that works, give it to the police.

I have a found iPad. I've tried giving it two separate Police d[epartments, they're not interested

Then you have a paperweigh. Sorry Apple works with law enforcement but not with the general public for these issues.

I just called Apple. I found an iPad and want to get it back to the registered owner.

Apple will do absolutely nothing. I am appalled. They have the owner's email and won't email them on my behalf.

They are unwilling to help the owner. I am really disappointed. I thought this company gave a $hit.

You aren't really thinking, are you. You say you 'found' an iPad. Substitute 'stole' for found and that will tell you why Apple will not get involved. They don't know you from Adam.

I am not suggesting for one moment you stole the ipad, but hopefully you can now see why the police are the only real option.