CAUTION: Acids are very dangerous, especially concentrated acids. So I want to see gloves and GOGGLES PEOPLE!
Getting your hands on Sulphuric acid is much easier than you might think, there's probably at least a liter of it in your car right now! Yes, battery acid as it's commonly called is sulphuric acid. I'm 'privileged' enough to live near a recycling centre where every weekend scavengers are allowed in to take whatever their grubby mitts can carry, and I was one of them. You can find used car batteries at any dump or recycling centre of probably in your shed.
Getting the acid out is an simple as unscrewing the caps and pouring it into a container (NOT a metal container as acid will happily dissolve through most metals). However the acid will be contaminated with lead and carbon. Leave the acid to stand until most of the particles settled to the bottom and carefully pour the cleaner acid into another container (again, not a metal one). If you're patient you can filter off the acid through a coffee filter to get rid of all the lead particles.
Now to concentrate it, this is a simple evaporation process but you'll need a bit of head too as sulphuric acid is very hygroscopic (that means is absorbs water from the air easily). Place your acid in a glass or ceramic saucepan and place a lid on top of it as the acid will spit. Gently heat it until it simmers and keep it at this temperature. The water will evaporate and your acid with a much higher boiling point will be left behind.
Once your acid is approaching concentrated levels the simmering will slow down and your acid may turn a murky brown colour. Keep heating for a little while longer. When it starts to fume violently it's done. Don't breath in the fumes. You can test it by poring several drops onto a small pile of sugar. If it turns black and steams, it's concentrated. This acid will do more or less the same thing to your skin so gloves please.
When you are happy with your acid you can pour it into a plastic container with an air right lid for storage. The container needs to be plastic to resist attack and air tight to stop the acid absorbing moisture from the air.