Almost all of your online hobby shops also sell ca. When I place an order online I usually order in a couple of extra bottles. Keep your unopened bottles in an unheated part of the basement (or refridgerator ) for long term storage. Just let the ca get to room temperature before using it. My wife recently found a 2 year old bottle of thin ca in the refridgerator I had forgotten about. It works fine.

DO NOT store opened bottles of ca in an unheated area of the basement OR the refridgerator. It will form condensation inside the bottle and can cause the whole bottle to "kick". Keeping open bottles in your workshop is normally OK. I have my winter workshop in the basement of my house (temp stays about 55 degrees ) and I have had no problems with open bottles kicking. I have 1 bottle of thick ca that is about a year old and except for being a little thicker, it is fine.