The Mayor's office jas a list of BMR units. Go to sfgov.org or use the link at my website. Plus there are many new construction complexes that are offering BMR units. But the fastest way would be to ask an agent to give you a list.
You can also have an agent create a property search for you in the SF MLS based on your price range. There will typically be some listings on the MLS since this is another marketing site for agents.
Or you can do a manual search at: