Aside from the conventional on-market routes through estate agents and auctions, speak to local letting agents too. They may have clients that are actively looking to dispose of investment properties or are considering selling.
We often sell properties off-market with sitting tenants directly to other investors. The benefit is that the selling landlord has rental income until the lease expires, and the new landlord has a fully managed, revenue generating asset from day one. Both parties have no void costs or liabilities.
If you are set on a particular street, you could have your Letting agent approach the owners to see if any would consider selling their property off market.