it sounds ridiculous, but I bought all mine from Ikea! I had the same problem as you, I couldn't find a decent one anywhere. Accidently found a great one called Hedera Helix on a window shopping trip and I couldn't be happier with it.
Most ivy's are fast growers anyway, but I chose this one because they have lovely variegated leaves which turn a lovely red in winter. I use it to cover the wall around my garden, and three plants has been enough to cover a stretch about 20feet long in just over a year.
Good luck with your search!