Just knocking on a neighbors door can land you a deal.

Needless to say, after closing I was working on the property when I heard a knock on the door.

As for off market, try driving for dollars, direct mail marketing, skip tracing phone numbers and cold calling, door knocking, anything you can think of to get in contact with owners and seeing if they'll consider selling.  

Next, with Covid-19 I feel door knocking may not be the way to go in order to move forward in the process.

Hello @Jake Freeman,Cold-calling, postcards/letters, and/or door knocking are good ways to start.

But upon transferring the home, I would like to knock the house down and build a new home on the land.

I would personally try to negotiate with seller about the “assignment” on this too and just be upfront about you’re not getting a commission on the deal with the seller but they should be aware moving this deal with seller financing through a wholesaler- there would be an assignment fee (the kept down payment of 3-5% usually) Ideally that 3-5% should be yours then to retain if you do seller financing as with anyone else they would lose it (pay it out) too it seems likeSo maybe that should be leverage for you in an amount knocked off the purchase price - therefore helping over the terms somewhat.

The last time I knocked on the door she opened it and tried to close it in my face.

Knock on her door and tell her what you found on Facebook.

We opened it up and the smell just about knocked us over.