In many cases just say excuse me but if that doesn’t work you can always speak with the driver, even blind people know they aren’t supposed to block the isles or other seats. He my simply not know that he is doing this, or in rare cases is just being rude

The man you encounter may still have some vision despite being blind, i.e. visually impaired or severely visually impaired. You may be able to attract his attention by waving at him while politely greeting him.

I think asking the bus driver is a good idea. If you notice him interacting with someone, maybe you could tell them? "Hey, I noticed you are friends with the man who sits in that seat. can you let him know I'd like to use the other disabled seat?" Do you also use a cane? Is he on the bus when you get on, or does he get on before you? If he's already there and you use a cane, can you tap his foot with the cane and say, "excuse me, I want to get to the other disabled seat?" I agree you don't want to startle him or upset him, and you also need to sit down. He probably doesn't realize he's blocking.

I'm probably going to get downvoted to hell, and should have chosen a less controversial stance for my very first post, but ...
Please, just *talk to him*.

It is very common for sighted people to want to interact with anyone but us blind folks. This is a huge issue any time we have a guide with us, because they will always speak with the guide. Same goes if there is any family member, partner, friend, etc. close nearby. I'm sure many of us know what an awful feeling it is to be treated as if you are not only blind, but also deaf/unable to speak/straight up stupid.

I wouldn't know how loud this fellow's music is, but I have been using headphones for screenreader use nearly all my life and am thus perfectly able to still hear my surroundings while wearing them. He might be the same. If so, just approaching and greeting him should be enough. If you want to make extra sure that he'll know you're talking to him, you could say something like "Hey there, friend with a cane!" although perhaps others might disagree on that one.

And if not? Honestly, a light tap on the shoulder will not hurt him. Simple, kind human touch* is not assault, and the fact that good people have to worry about that because of the assholes is saddening. Lightly tap him, and when that draws his attention, explain your situation and, if that'd make you feel better, apologize for not being able think of a better way to get his attention.

*Obviously blind people are subjected to a lot of touching that is only kind on the surface, such as being randomly grabbed and dragged in whichever direction the "guide" thinks they ought to go. That is wrong, as is any "help" given without asking if the helpee wants it first. Aditionally, any sexual and/or violent assault is obviously awful. But the intent of a shoulder tap is obviously an innocent one, and thus should not be upsetting to anyone but the most touch-averse.

And then, once you've got your seat? Ask for his name. Chat with him a little. Because trust me, you are far from the only person terrified of approaching him — as paradoxical as that is, given that it is much more challenging for blind people to approach others than for sighted ones. So heck, he might welcome the company, and you might gain a new friend.

Obviously, if conflict does arise — such as if the blind guy's cane turns out to be a sword in disguise and he starts madly waving it around — do approach the bus driver instead. OK, that is a goofy example, but of course a blind human is just as likely to be an asshole as any other. However, I am pretty certain it'll be just fine, and indeed go so well that you'll feel a touch silly for not just taking care of it sooner.

Alright, time to see how well Reddit handles text walls ...