Every company. Figure out what companies you are interested in, find people who work there, and write them a nice email telling them that you are interested in interning at their company and whom they think you should reach out to to talk about it.

One other interesting way to approach this issue is use LinkedIn to figure out where people who went to your undergrad school are now working. Find people who now work at the companies you want to intern in. Do the above (write them a nice email asking about their internship opportunities).

The key here is not to write 1-5 emails or to write 1000 to 5000 emails. The key here is to write about 10-20 emails that are hyper-specific to each company and each situation. What you are looking for is responses at this point, not internships.

Once you get a response, you can get started talking to the right people.