eBay is always a good place to start. There's a large selection of high quality wire on there. You just have to know what to look for, and use the right keywords. Searching the descriptions also helps to find the right wire. Many DIYer in here actually buy their wires from eBay sellers. The price is often reasonable too. You just have to keep in mind that Canada Post charges 8.50$ as import duties on orders over 20$. I just make sure my orders never go over 20$.
Parts Connexion are great to make business with. Don't hesitate to send them an email if you need information. They reply quickly and have an amazing service. This month they offer 20% off "almost everything", which makes it a nice time to buy wire from them. When they send you the invoice, just make sure they applied the discounts properly.
http://www.partsconnexion.com/wire_hookup_main.html
They have a small selection though.
Edit:
From Canare's page description:
The L-4E5AT is not flexible, and not recommended for headphones. The L-4E5C is a small, flexible cable which is often used and recommended for headphones. Both are shielded.
Their individual wires are not the same. The 6AT is a 22 AWG (larger) with 16 conductors. The 5C is 23 AWG (smaller) with 30 conductors. This alone makes the 5C much more flexible. Then there's insulation thickness, which I believe is thinner on the 5C. This too would make the 5C more flexible.
