David
I have found some off cuts, these were from Marlin as I asked for them to be supplied.
Large ID 22mm OD 28mm
Small ID 11.5mm OD 15mm.
I may now if doing it again use heater hose the whole way rather that making a join in the tunnel.
I am sure there are many places where you can get hose, but this company makes bespoke hoses to order for sensible money, only my view.
http://www.thhs.co.uk/
Steve