I presume you are talking about the hose that routes to the passenger side of the heater box.
Give CL a call and talk to Ian or Joe. You can buy this hose by the foot. It is metric but don't remember the size. The oem has a braided cover and fits through the firewall easily if you lube it with dish soap or 409.
I just did this on my Spider. The routing is as noted above.
Thanks Gary. By CL do you mean classic Alfa? The removal was not difficult at all.
1984 Moto Morini 3 1/2 Sport
1990 BMW GS100
1991 Bimota YB10
2001 BMW 525i Touring
2007 Mercedes R350 AWD
2004 BMW Boxer Cup Replika 193/300
PAST RIDES(abbreviated list): 1969 Spider 1750, 1969 Berlina x2, 1974 Spider x2, 1979 Spider, 1982 Spider x2, 2001 Jaguar XJR, 2011 BMW 328i, 2002 BMW R1150R, 2004 BMW Rockster Edition80 169/2003, 1968 Firebird Convertible, 1968 BMW 1600