You can get plant-based milk at pretty much any supermarket store, as well as other vegan products.
The only difficulty that may occur is if you are living in catered halls where there may not be much variety in terms of vegan products, obviously this depends on the uni.
Honestly though there's plenty to eat/make meals from with fruits, vegetables, pasta, beans etc. And I wouldn't base my uni choice off the availability of vegan food as it's all quite easy to manage. Now if you're talking about restaurants that will be a bit different as you'll find a lot more vegan friendly places in cities in comparison to small towns.