In this quest, Neel Gymont asks for 4 ingredients, two of which are bittergreen petals (ingred_bittergreen_petals_01) and hypha facia (ingred_bc_hypha_facia). In the Aanthirin and Roth Roryn, the former are very rare while the latter apparently non-existent. Thus I suggest that the quest add the topics "hypha facia" and "bittergreen petals", and that alchemists and scouts in OE and Andothren (or maybe on the whole map 4) have some moderately helpful responses:

bittergreen petals:
Bittergreen is a common plant on Vvardenfell; it grows in particular abundance in the West Gash. With its large bulb and its many sprouts growing in all directions, it is hard to miss. Its alchemical uses are rather scarce, so it is rarely cultivated.

hypha facia: [minor rephrase of vanilla]
Hypha facia is a light brown shelf fungus growing on the trunks of trees, mostly along Vvardenfell's Bitter Coast.