The VA Foreign Medical Program(FMP) covers service-connected, awarded disabilities overseas.
You can register with VA-FMP from any country. All you need is a computer and internet access:
You must ensure that there are clinics and hospitals that accept VA-FMP in the overseas location where you live and they are willing to bill VA-FMP directly. If not, you must pay for all medical services received and submit a reimbursement claim to VA-FMP.
The catch here is "Service-connected awarded disabilities". If you do not have service-connected awarded disabilities, you are not covered by VA-FMP overseas.