Summer internship post-grad?

Currently a rising senior at a target. A bit iffy on what I want to do after graduating but I'm planning to apply to a couple masters programs in the fall/winter. I want consulting as a fall-back so recently I've been looking into applying for summer internships at MBB-type places, with the hope that I could maybe go for a return offer if grad school apps don't work out (also ofc some summer income would help with grad school expenses). But I'm new to this industry and information on eligibility for these summer internships is really confusing... seems like a lot of them might be open only to rising juniors? What should I do and where should I look?