Where to get large sheets to cover the floor/carpet? (stores, sell)

[ny123]

We need a large sized plastic--or other materials--sheets that are large enough to cover some 5'x5' (about 25 square feet) of the carpet floor, to protect the carpet while someone practices his barber skills. Where can I get such huge sheets? Obviously it should be cheap for such purpose (to be disposed after one use). What stores sell such?

Thanks in advance.

[motormaker]

Hone Depot or Lowers sells tarps that come in many sizes. How about a old double or queen sized sheet?