Hello I want to make these pepper rings and I can not find the brown mustard seeds it calls for, is there any thing I can use as a substitute like a prepared brown mustard or leave them out? Here is the recipe

Mustardy banana pepper rings
2 lbs banana peppers
5 c. White vinegar
2 c.water
1/2c.sugar
1 Tbl dry mustard
4 cloves garlic smashed
1/2 t. Turmeric
4Tbls yellow mustard seeds
4Tbls brown mustard seeds
(I'm condensing instructions)
Mix in everything but seeds bring to boil to desolve sugar simmer 5 min. Discard garlic.
pack peppers into 4pint jars, then top with a Tbl. Of each seed.process in bwb for 10.min let stand a week before eating.
I thought these would taste like the prepared pepper mustards that everyone is making around here with hot banana peppers but on the safer side! Any help would be appreciated. This recipe came from Better Homes and Garden canning and preserving. 2014 . Thank You, Brenda