Here's a quick walkthrough of how to find the closest congressional district office for your representative on Congress.org. Click here
Enter your ZIP code.
Click on your congressional representative. Make sure that it's your congressional representative and not your Senator or state legislator.
Click on the Contact tab for your representative.
Once you've taken those steps, you should see your representative's local district office address. Some representatives have two district offices, so go ahead and click on "More District Offices" just to make sure you see all your options.