I'll put this here just in case anyone has the same problem and is searching for an alternative part in future, as the original part is no longer available from Fiat.
This is for hose #4 in the pic:http://homepage.ntlworld.com/sinister/coupe/crankcase_breather.jpg
Got this sorted now, went with the fluoro lined silicone hose from www.autosiliconehoses.com
1 x Silicone Fuel & Oil Fluoro 90 Degree Elbow Hose - 19mm
1 x Silicone Fuel & Oil Fluoro Straight Hose - 1 Metre - 19mm
1 x 19mm - Custom Alloy Straight Hose Joiner - 50mm with Beaded Ends
With discount code "ASHHOSE" came to under £40 inc. next day delivery.
They only have the fluoro lined hose in blue, but otherwise it's perfect.
The 90 degree elbow goes from the output of the oil separator tank around the back of the block and ends under the thermostat, where you use the joiner piece and then less than half of the 1m hose to bring it down to the intake before the turbo.
At least this will stop the flexy intake hose before the turbo getting covered in oil vapour (as it has been on every 20vt I've ever looked at) due to the original hard plastic Fiat pipe not sealing 100% against the plastic joiner. The silicone hose tightens down properly and seals 100%.