Not counting my "cottage daylilies" (long story) I started purchasing some from the local daylily society annual sale in mid August (around here). Wonderful prices, plants, and you know they grow in your area. I know the local society is about $5 annually to join - although one doesn't have to be a member to go to the sale.
Also, look into joining the American Hemerocallis Society. I got a voucher for my first year membership, which I then used at a participating seller, and got some beautiful more expensive daylilies last year. I happened to use my voucher at Maryott's and was very impressed.
Plus, check out the classifieds here on the forum, I just purchased and received some large clumps from a poster here.
Enjoy the addiction! ~Jan