Winter Saison? Hm, this is an interesting recipe. It's definitely an experimental beer rather than an attempt to make something spot-on style, so it's perhaps not crucial to use exactly what they did...as such, I'll give you what I think would work best there.
As cyraxx pointed out, the grain bill will make a fairly dark beer, so we don't need to worry about color. Piloncillo and jaggery sound interesting, but I'm not sure I can recommend it as I've never used them in a beer before. I suspect the result would be interesting for devoted beer geeks, but may be a bit harsh for others. But I'm just guessing. The sugar you linked to would work pretty well, but may get lost in the spices and Saison flavors. My choice would be to use a homemade dark amber syrup, though the D2 would also be very good. Dark fruit and toffee flavors aren't bad things to have in a beer that uses Carafa II and Special B....