Vapor Barrier???

Is it for the sub area? Any plastic roll will do. Just make sure you secure the plastic, some people use rocks or bricks, w prefer to stake them down by bending insulation wires and satking down each corner of the plastic. Not fun, it's time consuming.

Inside or outside? Common vapor barriers are used under siding can be purchased from companies like Tyvex or any other house wrapping. For vapor barriers under the drywall... it has been my experience that 4 to 6 mil (millimeter) plastic works great, which you can purchase at Home Depot.

Inquire at Lowes or Home Depot