I store grains,crushed or not,in there sealed bags in the fridge for a month or more. I noticed midwest,for instance,sends smaller amounts of grains in tall narrow zip lock bags, I put them in a zip lock freezer bag in the fridge with the air burped out. They've been keeping just fine.
Other folks store their grains in tupperware containers in a cool,dry place with good results also. Some sites do have 1 gallon kits,like Brooklyn Brew Shop,& I think Northern Brewer.