Indian cuisine uses mustard oil. Maybe an ethnic Indian or Asian market would carry it.

Mustard is a condiment made from the seeds of a mustard plant (white or yellow mustard, Sinapis hirta; brown or Indian mustard, Brassica juncea; or black mustard, Brassica nigra).

POTATOES.

There are different types of Mustard. The common type of Mustard is

1. Black Mustard-- Brassica Nigra

2. Garlic Mustard-- Alliaria Officinalis

3. Hedge Mustard--Sisymbrium Officinalis

4. Tumble Mustard-- Sisymbrium Altissimum