I purchased the Essentials Kit off Amazon when I was first inspired to try D&D in the classroom.  

Apply to the D&D Beyond Educator's Account and to get a school kit.

The Lone Wolf books (bottom left) are choose-your-own-adventure books I won in a draw from a free fantasy newsletter, Rediscovered Realms, which I signed up for when trying to figure out this D&D stuff.

The Dungeon Master's Guides, Player's Handbook, Monster Manual, Tyranny of Dragons adventure guide, the miniature figurines (top), the mountain of dice (in my desk drawer), and the flyers and monster stat cards (bottom) came from two wonderfully supportive local businesses: Tap Games and Authentic Dungeons. Pop in. Look at how cool their stuff is. Chat with them. They are friendly and fun folks.

• Just ask. Odds are, local businesses that deal in tabletop games will be huge fans of whatever you plan to do in your classroom and will likely want to help you.  

• They also likely have some creative ideas on how to make your dream a reality.