If you can’t find decent-sized jars for pickled onions or other pickled food items, nip to your local chippy and ask them to keep their pickled onion, pickled egg and pickled gherkin jars for you. In my experience they are happy to do so, because they only throw them away otherwise. You can get the jars for free, and help the environment by recycling. These tend to be good quality jars, too: very large, and they already have acid-proof lids!
Note: this is a great tip. Anyone who pickles will know how expensive these giant jars can be if you buy them new. The acid-proof lids are a boon too: vinegar can react with metal lids, so people who pickle will often place layers of cling film beneath the lids to act as a barrier.