Mixed seeds grown indoors can produce veg from different seasons. You could try filling a portion of your greenhouse or a bunch of garden pots set indoors (farm cave counts) with mixed seeds and see if you get lucky. That way you don't have to wait for the night market in winter.
Also, check Gus' dish of the day at the salloon.
Or you could take the extreme route and marry Alex. He gives hashbrowns as one of his gifts.