I need a spring for my radiator hose. Where can I find one?
The thought that a spring is needed in a radiator hose is a common misconception, that springs (pun intended) from two events.
The first is that many (although not all) lower radiator hoses on the production assembly line had springs in them. The reason for this was the method by which the assembly lines filled the cooling systems. To save time, a special vacuum/fill fitting was placed over the radiator fill connection (the place where the radiator cap would eventually be placed. A vacuum machine was turned on to evacuate most of the air out of the cooling system. Once completed, the fill portion was turned on to introduce the coolant into the system. This process avoided entrained air preventing the system from being completed filled. The purpose of the hose spring was to prevent collapse during the vacuum portion of the fill cycle.
The second part of the story that has led to the "I need a spring" myth is that some people have observed their lower hose collapsing when they rev the engine. This is the result of a clogged radiator or a cooling system that has not been brought up to standard operating temperature. If an engine is revved up while still cool, there is only atmospheric pressure in the system. It is possible for the lower hose to collapse slightly due to the water pump drawing water out of the lower hose faster than the gravity-fed water from the radiator replaces it. Once the engine has been warmed up, the coolant system operates under pressure and this condition doesn't exist in a properly maintained cooling system. However, if the radiator tubes have restrictions, as the engine is revved, the water pump pulls coolant from the lower hose faster than water can trickle past the clogged tubes. This can result in a reduction in internal pressure that would cause the hose to collapse.
Note that the events that lead to the thought that "I need a spring" are based on either an insufficiently warmed up engine or a clogged radiator. The spring does not take care of these events. It merely masks a symptom. If, after your vehicle has reached normal operating temperature but you experience a collapsing hose, have your radiator tested.
As an additional thought, have you ever wondered where your original spring went? Did you ever find bits and pieces of it scattered throughout the cooling system? Being made of ordinary steel, they corrode with time, small pieces gradually breaking off and either scoring the water pump impeller, tearing the water pump seal, or clogging the radiator. They aren't necessary for the functioning of a properly maintained cooling system.