Unless you just have to have the OEM hose, just about any 5/8" ID flexible hose should work there as long as it doesn't kink when it's bent.
The Samco Silicone radiator hose kits included a piece of flexible hose in the same color for that Idle air bypass hose.
Try going to the local Auto Zone or similar and ask to look at their radiator and heater "hose wall", you might find something pre-bent that will work.