We go to the local ag store, Agway or Blue Seal for greensand, bloodmeal, bone meal, etc.

Why do you think you might need greensand? Did a good reliable soil test show some nutrient deficiency that greensand might correct?
Keep in mind that any nutrients in greensand need an active Soil Food Web to release them and get them to the plants and that Soil Food Web needs organic matter to live and function in and most often adequate amounts of organic matter will supply all the nutrients plants need to grow strong and healthy.
Greensand, and rock phosphate and other similar materials, are now being considered as not sustainable materials and require too much of non renewable resources to mine.

Mining and powdering limestone isn't sustainable, but a lot of people will starve if we don't do it. So I wouldn't worry too much over buying some greensand. It is a fine source of slow-release K.

I haven't added it to my beds for at least 10 years, maybe 12 to15. I like to add it because of the trace minerals. I am going to top dress with compost as I always do.

It has some traces, but is mostly adding K, from what I have read. That is how it has acted for me as well. For broad-spectrum you'd be better off with a deposit like azomite.

I added greensand to my soil many years ago and found it made no difference in the soil tests that just adding compost would not also add. Since no real benefit was seen, in soil tests and in plant growth, I determined there was not real good reason to spend my money on the stuff.
A good reliable soil test will tell you if the soil needs any.

Quality compost with a variety of ingredients generally has a very good micro-nutrient content, and requires no mining, grinding or shipping. :-]