Aye bikeplantation,
Try your local hydraulic oil pipe supplier, ask around local motor factors, or visit Pirtex [pricey!]. You are looking for reinforced oil supply hoses. You maybe offered black rubber or nylon reinforced clear plastic hoses. The former is strong and less affected by sunlight, whilst the latter is strong but maybe affected by sunlight/heat and become hardened, you can also view oil circulating through it! Finally clear maybe available from B&Q, but you will need to get them to confirm it's properties and spec!!!!!
Agricultural engineers or plant hirers may also prove helpful.
I hope this gives you some leads.
Regards, Bill.