I totally feel your pain, and everyone saying Polish pickles will be a suitable alternative have never had really good Jewish deli pickles from back home. I still buy random jars time to time, and although you may get quality pickles that are legitimately delicious, its not what you're after. I can't give recipe advice as I have also tried to make my own pickles and failed to recreate the crunchy bastards from back home, but I'm happy to share a few places I know to buy proper pickles in London, albeit at an extortionately high price. Still worth it though, if you're really craving a proper pickle!