Buy marshmallows on sale and freeze freeze them in bags until you are ready to use them. They defrost and work quite nicely in recipes and keep longer.
Substituting Marshmallows and...
Freezing Seafood Dips and Spreads?
Marshmallow Crisped Rice Treats (Giant Roasters)
Substitute for Marshmallows?
Freezing Baking Soda and Baking Powder?
Making Homemade Marshmallows