You can get flexible oil/fuel hose in various sizes including 5/16 from eBay see
This Link.
The one listed has a black nylon braided outer, followed by a braided steel middle followed by a synthetic rubber inner so very strong and available in a variety of sizes.
For clamps I would use standard jubliee clips, make sure you use the correct size. Better still get hold of a crimping kit with appropriately sized ferrules.