Needle Receiving Tube for tatto is a good option for heater tube
https://www.ebay.co.uk/itm/316L-Stainless-LARGE-00-Guage-10mm-Piercing-Needle-Receiving-Tube-/371434490356
Or you can get some Grade 2 Ti fairly cheap. I also looked into SS or Ti hose fittings,( 50mmflat disk leading to a 8mm ID...