Perhaps it is wrong to assume you absolutely cannot find these vegetables in America. It would be more correct to say: You might find these vegetables at very specific ethnic markets or very expensive gourmet markets. Nevertheless, don’t expect to find any goosefoot lurking in the produce aisle at Walmart.
America is actually home to a few vegetables some regions may know very well while others regions might not recognize them at all. For example, although most New Englanders are familiar with fiddleheads and dulse, a resident of Iowa might never have heard of them. A few years ago, vegetables like kohlrabi or celeriac seemed foreign to many, but as trendy, food-forward restaurants began adding such items to their menus, this is no longer the case.
Regional vegetables don’t stay secrets for long, especially once their nutritional potential is discovered, so you might see these vegetables at your local Whole Foods sooner than you think. But until then, you’ll just have to travel around the world for them.