You can search Angellist for remote and internships I think.
I'm not sure about a site dedicated to this, but as @aviaryan mentioned you can search on regular job boards and use the right filters.
For example, @levelsio's remoteok.io has a section dedicated to only remote internship jobs.
Having said that, I would advise against doing a remote internship. The beauty of an internship is that you get a chance to work with more experienced people and see what it's like to work at a company. I think by doing this remotely you lose out on much of that.
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