There are several types of Tygon.  The one we use in the Lancair fuel system is F-4040 and it would be a good choice for hydraulic fluid (I think).  Here's a link to the site.

http://www.tygon.com/tygon-f4040a-tubing.aspx

Du-Bro packages this stuff as fuel line for model aircraft.  It is sold as Tygon and marked as F-4040.  Any decent model aircraft hobby store will carry it in multiple diameters and sell it to you by the foot.

- Rob Wolf