I buy my Sea-90 from 7 Springs Farm Supply.
https://www.7springsfarm.com
I agree with you about the difficulty to find it locally so I can just go buy some and not pay shipping. To bring shipping costs down, I'll get several 50lb bags, some bags of kelp, and maybe some other things as well so the pallet freight charge gets down to under $20 per item. It may be a lot of money up front, but it'll last me a year or a little more. There is a distributor 2 hours away from me so I can save on shipping and go get it, but I have to buy 2000lbs at a time. I'm not opposed to that as I would need almost that much to apply to my small farm pastures, but, my wife and I are being careful budgeting and prioritizing our funds so that kind of thing goes to the bottom of the list right now.
I have a 3,000 square foot annual vegetable garden, plus a small amount of fruit and berry perennials. I'm also interested in offering mineralized water to my flock of 8 laying hens.
How much Sea-90 would I use in a year?
The application rate for soil use according to the manufacturers website is 50lbs to an acre. At 43,560 square feet in an acre, I'd imagine one 50lb sack would get you through several years, and provide delicious salt for cooking. I've been using sea-90 for years as my go-to salt for foods and love it. If 50lbs is too much for your needs, the maker has a 10lb bag plus a 1lb bag for cooking for under $30. I don't know what shipping would be as it varies on location, but this may be a more economical way to get trace minerals into your annual vegetable garden.
https://seaagri.com/product/combo-sea-salt-table/?v=400b9db48e62
Hope this helps!