Barbwire is not as easy to find. But taking a bat, making a crown of construction nails and tying it together with a lot of glue tape (otherwise, ahem, the nails will make the bat shatter) - the classic way is always the best.

You can also bite off nails’ heads with metal scissors, and use a good enough pipe, and make a very basic and close-range firearm. But that takes some experience and awareness of the dangers (like killing yourself occasionally when the thing blows up).