I have three non-Nestle branded/made tins of condensed milk here. Peak, Alaska and Grace brands. Sainsburys sells Grace, but not with the other condensed/evaporated milk etc, it is in with the caribbean foods. Peak and Alaska are readily available, at least in London, from cornershops/small grocers.
However, all condensed milks are not created equal. Using exactly the same other ingredients/pans/utensils Alaska and Grace behave very differently when making fudge. Alaska reaches 116C (soft ball) very quickly, but it is very difficult to get the same recipe made using Grace up to temperature.