"Volunteer research assistant" is a problematic term. It sounds like something I should be asking HR about before I could agree to anything, and you being overseas would make things even messier. "Research assistant" is a job title, and being one might make you a member of the hosting university. Not asking for money means that no funding is needed, but this doesn't necessarily make the paperwork any easier. Also, some (many?) people feel that it is unethical to volunteer for something others would expect to get paid for.
In my eyes, it is a completely different picture if instead you seek to collaborate with a researcher on a particular project. This wouldn't put you in any kind of hierarchical structure, and being an independent researcher is a perfectly valid hobby.
The second issue is the question what you can actually offer. Most opportunities where inexperienced people can contribute well are in-person tasks (cleaning laboratory equipement seems to be a popular task to give to students seeking research experience). In my area (math/TCS), it would be very difficult for someone lacking experience to make any positive contribution, and accepting to work with a stranger would make little sense to me. Whether you have something to offer will depend both on your current skills, and on what exactly people in your area do in their research.