Look for vickers belts, they are out there. You'll likely have to post a want to buy ad on one of the machinegun boardsl like Sturmgewehr.com , Subguns.com, or gunboards.com. The vickers belts were originally made for .303 but 8mm will work in them too. You need to stretch the belts a bit by loading them and letting them sit. Once stretched they work very well. I use them in my maxims with great result. You might be able to find an original 8mm maxim belt but they cost substantially more and aren't something you'd want to use for actual shooting.
Hope that helps