One potential institution would be Bauer Media, which is a large media institution based in germany and as they seem to almost have a monopoly on rock and alt rock magazines, also my magazine is similar to some magazines that they already produce, such as Kerrang. I also think this because they already distribute hundreds of music magazines, from almost completely unknown magazines to massively popular magazines, so they would be more likely to distribute my magazine than a institution that only distributes popular magazines
Another potential institution could be Time.inc as they produce NME but I think they are a lot less likely to distribute my magazine as NME is the only music magazine and the majority of magazine the distribute are lifestyle magazines.
I think my magazine could be distibuted both in paper copies and online via subscibtions and in stores. I believe this because my target audience include both people who buy magazines in store and people who buy subscriptions online