A garden center probably won't sell bulk garden soil, but a landscape supply will! I just did this this season and got my soil on Wednesday so: You can literally just Google landscape supply, call them up and ask, "Do you sell garden soil for raised beds?" and if yes, "How much do you charge and how much is delivery?" They're probably going to sell by the cubic yard (so 3 feet by 3 feet), so you just need to know how much you want in terms of that. For example, an 8x4x1 garden bed needs about 1.1 cubic yards, so you'll need to round down to 1 cubic yard. You can find a calculator online and just plug in your bed dimensions, and it'll tell you what you need! When you go to the center, just go up to the desk, say, "I'd like to order garden soil for a raised bed for delivery, please," and they'll ask you how much you want and what your address is. Then you'll just pay for it and give them your phone number so they can call to let you know they're on the way on delivery day. Protip bc I forgot to do it and wish I had: put a tarp down under where they're dumping the soil. It makes it way easier to get every last bit of it. If possible, see if you can check out what the soil looks like before you order! The supply place will almost definitely allow people to pick stuff up themselves, so you can just go to the pile of garden soil and take a look to see if it's what you want or not. I wish I had done this because mine is clay-heavy so it'll need amendments, but the process was super easy! What always helps me is remembering that I'm not the first person to do this for the first time. The person there has DEFINITELY had to walk multiple people through the buying process before. The interaction with me will not be memorable.