I think the ones that do have them,made there own.
You would need some mandrel tubing.And some silicone
connectors tfor the ends.
I am getting ready to make some for my SC.Some of the
tubing I looked at.It could be done from about $100.00
to over $200.00 for the materials.silicone connecters
about $8.00 to $20.00 each.Then add the labor.