Ok so I picked up the GM screen and the adventure module Debts to Pay. One question I have is where is this planet Bargos the Hutt won in his card game?

Gavos, at least that is what it reads.

The only think I see on the Galaxy Map in the Core Rulebook is Garos in gird square P7.
Is there a typo? Is this the planet they were talking about?

If not where is this the planet?

I can't help you with maps but there are BILLIONS of stars in the galaxy. I wouldn't be too surprised if you find me ton of a new one here or there.

That said, every time I go to starwars.wikia.com to look up a planet, I hear grid coordinates that reference the Star Wars Essential Atlas. I'm blind but that sounds like a map to me!

Gavos is here: http://starwars.wikia.com/wiki/Gavos_system

It says grid q10. Hope that helps.

The planet is where ever you as the GM decide it to be.

As a general advice, I would recommend taking the adventure module source material as a guideline rather than hard rules carved in stone. Adjust it to what suits the PCs story and your personal interest. And be prepared to fill in the gaps in details and logic yourself.

If you need to find a planet and you need to know its canonical location, there are two options. Either search from wookiepedia, and/or search from http://www.swgalaxymap.com/home/modified-map-page/

Not everything is in swgalaxymap.com, e.g. Gavos is missing. But with small work you can find its canonical approximate location using systems near by or sector data.

But, most important thing to remember is as Wolf808 said, planets and systems are where they need to be.But, it's ok to want to know what is the canonical location of planet, but you don't need to know.

The planet does not matter for the adventure. it could be anything you want, part of your campaign, or even a new planet. In my campaign I didn't even use a Hutt, or gammorians in the first part. But a Noble with some thugs. I even used a new planet for the mine and placed it in my campaigns sector

All you need is a person who is in debt, who now has a deed to the mine and is desperate to get some liquid assest from it to pay off his debts so he doesn't get beaten up by Thugs he owes money to