There are no 504 plans in college and the standard for accommodations is lower at that level too. The accommodations cannot pose an undue administrative or financial burden and cannot substantially change the program. Some disabilities offices serve as a filter in some ways. Once a kid registers with proper documentation, the disabilities office will give the student a letter for each professor. The letter may or may not state any actual accommodations and may or may not mention the disabilities involved (but they are generally accessible in a file in the office). The student must then talk to the professor and negotiate, basically. There is still some discretion for some things on the part of the professor (for absences, for instance)
In our experience, often there are other people on campus who are very helpful. Deans who communicate with professors, medical folks, advisors, tutors. For that reason, it can be hard to tell how good a fit a school might be before actually attending, and certainly hard before admission. It is true that smaller schools can offer more personalized attention to these matters, and they be wonderful even if too small to have an official disabilities office.
I personally feel that young people with disabilities should choose a school for the same reasons anyone else does: size, location, academics, “vibe.” The law is the law and they should have rights to accommodations based on documentation, anywhere. Some schools have more complicated systems that take awhile to learn, but overall, the ideal if for a kid to be able to choose a school for other reasons
That said, there are schools with reputations for being good learning disabilities, if that is relevant. Of course Landmark (and they have a summer college prep course too), and I have heard Curry and New England College are good. Maybe Lesley.
I think that people who can afford it sometimes hire a coach, who can work by phone or online as well as in person, depending. That is expensive of course, and we could never afford it, but it can make a huge difference.
So you might have to lower your expectations of what a college can provide, and also think about whether you want to make the disabilities office quality a criterion for where to apply- especially when you really cannot tell how things are going to go beforehand, that easily.