I just found both the GM Genuine heater hoses at Rock Auto. I missed the one the first time because I looked under Cooling System - Coolant Hose/Pipe, but just found both under Heat & Air Conditioning - Heater Hoses. Phew!Hmm looking at the GM online store it lists two different part numbers but ones discontinued.
95935067 which is the discontinued one. It’s the outlet hose to heater.
96958209 which is available. It’s the inlet hose to heater
You could measure the size of the pipe you need and see if some straight but flexible pipe could be used. Just make sure it’s not going to rub on anything.
Heater Inlet - 96958206
Heater Outlet - 954920002