You could do something like a Woodfordes Wherry kit and just brew one can at a time. Technically it would give you an 11.5 litre batch if you brewed it to instructions, but you could easily brew it short to 10 litres and it would still be good beer. That kit comes with two cans and two packs of yeast, so it's about as simple as it gets. You'd only need some priming sugar for your barrel/bottles.
If you wanted to do something more custom, then Munton's for example have various malt types as liquid malt extract (or dry), but might be better for you to provide some more info about the type of beer you want to brew...