I worked for a small medical and now it is closed. The person who owned this medical is also not in the country. I have my joining letter and salary slips as well as an experience letter. What can I provide more ?If you can manage to get experience from a company previously worked at (in the last 10 years) , use that. I was in the same situation as you. My previous employer was very helpful and got me out of the situation.
If you are unable to do so my opinion would be to locate your hiring letters / contracts, as many pay slips you can find, bank statements, company id (where I come from, some companies have a proper id, others do not) and mention the situation in the LOE.
If the company closure was public, do include as many news clippings / reports etc.
This should suffice. However, more experienced people on this forum can guide you better.