Here are 2 fern specialty nurseries that I have purchased hundreds of ferns from. Both have excellent products and are owned and operated by experts in their field.
deeprootsnursery.com
fancyfronds.com
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Rb

There is a nursery in BC called Fraser's Thimble Farms which has an excellent selection of ferns and ships all over. Their catalogue is on line.

I've only shopped there in person and of course am in the same zone; I guess you can only order from a warmer zone in spring.

Here is a link that might be useful: Fraser's Thimble Farms

Thanks for the suggestions, Razorback and Karin. These places look pretty good. I'll put them on my list of sites to peruse when I get down to the nitty gritty later this winter.

I'm going to try www.tripplebrookfarm.com this spring, as I am looking for some hardy ferns as well.

I can heartily recommend Fancy Fronds - Judith has a great selection of ferns, including a number of hard to locate varieties and she knows her stuff. She is close to me, so I don't do mail order, but a number of her ferns are now happily residing in my garden.

Come spring, I can dig you some ferns--I have lots:

Dryopteris spinulosa var. intermedia (Ostrich fern)

Dryopteris cristata var. clintoniana (Lady fern)

LMK--I collect orchids; maybe we could work out a trade for ferns.

Just wanted to report that I just got an order today from Big Dipper Farm, and am very impressed with them. Very healthy ferns, packed perfectly, fast shipping. I don't have any to compare with them, but I'd definitely order from them again. I got Champion ferns, Leatherwood, Beaded Wood fern, Ostrich and Christmas ferns. Was worried about the current heat, but these babies are in great shape in spite of it.

Out of curiosity, I just tried to pull up the www.deeprootsnursery.com site. Did they go out of business? I can't seem to find them.