Thanks for reaching out. YouTube Music is available in United States. You can signup by downloading the app from Google Playstore or the Appstore. Here's a list of available locations: https://yt.be/help/5W4Z . Hope this helps.
Thanks for the detailed info. While we don't have an ETA on this, we're always working on bringing our service to more platforms. Feel free to share your thoughts on what we could do better via in-app Feedback: Account > Send feedback. Thanks.