Body language coaching doesn't just exist, it's an industry. It is typically associated with public speaking, salesmanship, etc, and there are a lot of places (and books, and online resources, etc) to get training. In fact, one of the linked blogs in the OP, "Paging Dr. NerdLove", is completely dedicated to helping men who are bad at inter-personal communication with women (i.e. socially awkward) get better at it, which includes quite a lot of body language training.

It's reasonably well known that body language comprises a significant portion of interpersonal communications, so just like you'd expect with other languages there are quite a lot of resources for learning the language, if you take some time to look for them.

And of course, like any language, the resources are of varying quality and usefulness. But the general idea of "you get what you pay for" holds.