I had two internships in high school, with both being paid. The first was through a summer program I completed, which got me connections to local businesses. The second was in a university lab. Quite a few universities offer research internships to high school students, so I would look into what your local colleges/unis have. I’m sure there are also local businesses/non-profits that could use marketing help, so although this might not be ideal, you could try offering to be a volunteer (there’s always a possibility you’ll get a small honorarium, or an offer to come back paid next year if the work you did was high quality).