I made my own axle and timing case breathers the other week used this stuff
Polyurethane Flexible Tubing Pneumatic Pipe Tube - Any Size, Colour, or Length# | eBay
£8.95 for 25 metres seemed pretty cheap.
And a pair of these for the axles 1/8" BSP Male - 6mm Pack of 4 Swivel Elbow Push In...