Stir together vinegar, sugar, salt, coriander seeds, fennel seeds, peppercorns, red-pepper flakes, thyme, and 2 cups water in a medium saucepan. Bring to a boil. Add ramps; return to a boil. Reduce heat, and simmer until tender, 5 to 7 minutes. Remove from heat, and let cool completely, about 1 1/2 hours. Pickled ramps can be refrigerated in their liquid in an airtight container up to 1 month.