I'd try a piece of hose or plastic cut from a milk jug or similar and slide it under the existing clamp and then add a second clamp, not too tight, so the current clamp holds the plastic/hose patch in place and the second one keeps it tight against the leak and try it out. You don't have to wrap around the entire hose with your patch, but maybe loosen both current clamps and try turning so the leak is at the top of the hose, so you can get it nice and clean, then wrap electrical tape around the hose's leak and then add the patch and second clamp. Meantime order a new hose from your dealer to be sent direct to you.
Ooops, just re-read your post; you say it's leaking from the overflow tank? Could the tank be too full when cold? Have you tried tightening your radiator cap when the tractor's cold? Is the overflow boiling coolant when it is leaking?