I started freelancing as a sys admin 20+ years ago and have adapted my skills over the years to find myself having recruited a few for employers around Europe. Based on my experience, you'll find few positions that will suit your availability - I say few implying almost none but you might find the exception.
Firstly - SysAdmin is old school - I still use the term, but my sysadmin mates call themselves System Engineers nowadays. SysAdmins are the lesser qualified (using smaller toolset knowledge/experience and frequent repetitive work) I am told with a grin; the System Engineers are leading edge technologists.
Anyway... One of the main reasons behind few opportunities for you is liability - if you work from remote, you are under the wings of your local laws - The ability of an employer to prosecute you for misadventure would be both expensive and complicated. I'm not saying you would be of that nature, but best practice for employers business decisions is based around risk/impact.
Other risks that can apply are tax rules - for example within Europe many EU countries have a special 'chain law' which says if a business takes on a service provider (freelancer) and the freelancer fails to pay the taxes due, the tax man can work their way up the chain and charge the business. Thus, a business could carry the risks that you will pay all tax and your country, and their country could have different interpretation on what is due.
Then there is data security - giving you command line access is like letting you into the bedroom of the business - all sorts of stuff is available within seconds and employing someone to watch over you would erase cost benefits of undertaking your services.
Opportunity still exists, though: Research your local market for international consultancies. They use their international relationships to win contracts that require people like you. They charge a premium to these other businesses, take a huge amount of cream off, and pay you the remainder (still very profitable, but don't be surprised if they are making more than half of what they might pay you). It might appear they do nothing for that cash, but they are undertaking commercial risks that go with these foreign contracts.
Lastly - research more about being a freelancer - it can be rewarding, but the relationship with the business is typically not the same as employee/employer. I compare it to prostitution - you are hired and fired without rights, without pension, health or other insurances. If you get sick, it's unpaid; if you screw up, you could pay dearly.
I hope that helps. Best of luck.