I’ve bought untreated Redbor from Moles for the last couple of years on derogation. https://www.wholesale.molesseeds.co.uk/ Couldn’t find an organic alternative previously but this year I’ve ordered some organic Rote Krauser kale from Tamar instead to see what’s it’s like.
The other three, Moles above or Kings will probably have them if you’ve not looked already. http://www.kingsseedsdirect.com/. Unfortunately neither of them specify if it’s treated seed on the website so if they list something I want I’ve had to ask them before ordering. I’ve had stuff I had to remove from a pending order after they double checked at packing stage and phoned me to say it was treated.
I’ll recommend WPAK 1174 from CN seeds as an alternative pak choi to joi choi.
I’ve been growing its predecessor WPAK 1165 since 2012, and have found it to be superior to joi choi, 600gm to 1Kg heads, slightly slower to bolt and equal cold weather tolerance. I’m still using the same pack of seed I bought back then, so haven’t tried WPAK 1174 yet, but can only assume it is at least as good as WPAK 1165.
Tozers purple sprouting Cardinal always did well for me in the March to May cropping period, while not being a hybrid it was a very strong uniform variety, although Red Fire F1 sold me on hybrid purple sprouting, shorter cropping period but oh what a crop.
Mendocino through Moles is only available treated. Sadly this obsession to treat everything still exists. Redbor and Mendocino may be available untreated from Elsoms, but I doubt it, otherwise if you’re after enough it may be worth going direct to Bejo and finding out whether they’re available untreated via another European distributor.
Yes agree that Kings is good for varieties may need derogation if they don’t have organic, why grow Tundra when you could grow January King plenty organic seed available at a fraction of the price. The most reliable late winter cabbage ever invented we have grown it for over 40 years and it has never failed still cutting excellent heads despite a lot of heavy frost since end of October