How can I use a pre-existing AppleID with Mac App Store without a billing address?
If you want to use an existing Apple ID, you're out of luck. You need a card to be entered and accepted, so you'll have to pay for one or get a friend to trust you to add it and then remove it immediately after confirming your account for the store.

You probably also can pay a US bank to provide you with an account and debit card, but that can be more expensive than many find ideal. Many businesses sell addresses as well if you can't use one from an acquaintance.

You can usually make a brand new Apple ID following these steps:


https://support.apple.com/en-us/HT204034


It's generally a bigger pain to have two Apple ID, so I would encourage you to not set up a new ID just to avoid the temporary delay of getting a legitimate address and card for temporary use. 

Once you have your account verified, you can use store credit for just about everything on the Mac App Store. One note, that if you do this too many times on one device, Apple usually blocks new account creation on that device without a credit card. Unscrupulous people took advantage of that to manipulate app store ratings in the past.

Also, lots and lots of relevant details:


Can I download a free app from the App Store without a credit card?
How to use an existing Apple ID to download free apps from App Store without using Credit Card?
I have an Apple ID but it is not associated to App Store. I have tried to associate it, but it wont let me without a credit card. How to proceed?
How do you use an existing AppleID on iOS App Store without providing a credit card number?