I have wheaten marrans. I've got eggs in the incubator at the moment but I can't candle through the shells to check fertility. I won't be selling any till these hatch out and I can confirm that the cock is working properly. And they'd have to be posted, unless you're up in Dundee anytime? which isn't ideal. Last year there was a seller on preloved with three strains of Wheaton marrans. They were in Cumbria. North of Carlisle I think. I can't remember if they had a website.
I reckon you'll find closer, but if you are still eggless in 2 weeks let me know and I can post you some if you like?