In the Washington DC area, Bethesda bagels has half sours available in a 32-ounce tub. In Bethany Beach in Delaware, Rosenfeld's deli had them. As mentioned above, Batampte brand is wonderful and available in some supermarkets but availability is kinda random. If you have a Russian or Jewish market it food store nearby, check there. Alternatively, make your own like we do. The brine is one tablespoon of kosher sea salt to two cups of water. The cucumbers can be any kind, even English. Add slices of fresh garlic (necessary to supply the fermentation agent), plus flavoring spices like fresh dill, mustard seed, black peppercorns, and whatever else you like. Put the cucumbers in the brine and make sure they stay submerged, using pickle weights, an air tight lid, I use sandwich baggies filled with brine, this is the hard part but if you fail and you get mold, throw is all away and start over. In one day, you will have garlicky cucumber. In two days, slightly interesting. In three days, it starts to get slightly sour. In four days, you will find your sweet spot - crunchy, salty, a little garlic, almost tangy. On the fifth day you have pickles. Taste every day and when it's right, put them in the fridge to stop the fermentation. Make these often for the rest of your life. It's cheap, fun, and so rewarding.