Have you tried making your own condensed milk? I haven't tried this before but I have heard that you can use any soy/nut milk to make your own.
Soy milk is probably the easiest to access (where I live anyway). You could try combining 2 cups of soy milk with 150g of sugar (or agave syrup) in a saucepan over low/medium heat. Stir until the sugar has combined. Simmer for about 30- 40 minutes without stirring so the mixture doesn't crack. It'll have reduced to about 1 cup in volume and turned darker. Pour the milk into a clean jar/container and allow to cool before using. If you have any extra sugar that has crystallised around the edges of the saucepan try not to add them.
if you can find any soy milk powder you could substitute it for the milk powder in my condensed milk recipe already (the link in this recipe). And sub the butter for a lactose free butter/oil that firms up when cool. I only know of coconut oil but you might know of something you can use in its place (or try it without).