I have no idea why you are having trouble finding "plastic" for tube flies.ANY primary research on the internent will show a huge # of suppliers.Just find the nearest supplier of plastic products nearest to you .Johnson Plastics are great to deal with and will entertain small orders.Just ask for Polyethylene tubing in the I.D.andO.D. sizes that you require.If they DO have the "high pressure" variety that's the one to order !
If you know anyone that works in a medical research lab.Eppendorf disposable tubes( I believe they are used on centrifuges) are IDEAL for what we need !! However they come in batches of 5000 +
But you DID mention industrial quantities
BTW if you do buy any of the eppendorf tippet tubes I'll buy 100 of ya !!!!