How to learn sales and marketing?

Most of my career (30+ years), I have depended on job shops and
agencies to keep me busy, and I have been happy to pay them their cut
to do it (this was back when their cut was a little more reasonable
than the cut they think they're entitled to today).

Now, though, both I and the marketplace have reached the point where I
MUST learn how to do sales and marketing of software development
services, and generate my own clients.

That means I need to learn how to identify possible new clients AND
how to get past the HR departments AND how to do cold-calling in a
way that doesn't make me sound like an idiot over the phone.

Pure networking only takes me so far, in that most of the networking
contacts I have cultivated over the years have either moved on to
other things (my very BEST contact quit the business and opened a
security alarm installation company, and another one opened a
restaurant) or have dropped off the face of the earth.

I'm willing to pay money to take a course (preferred) or buy a book
(if no course is available) that will teach me this stuff.

Any ideas or suggestions for courses (online or in person) or books?

Thanks...