Transition between new and old drywall

I've got 48" high tile on 3 walls in the bathroom. Was going to just remove it, but it's laid in a thick cement base, so I thought I might just cover it with PVC beadboard instead (PVC to avoid moisture issues). Problem #1 is that I can only find small sections of the stuff at the local Philly stores, and they usually stock 36" height, not 48". What I need are something like 4 x 8 panels - does anyone know where these might be obtained?

Hi We are having some plumbing work done which is going to require them to get at the manifold behind the water heater in the garage. That wall has the ugliest green/white tile going half-way up the wall in an area maybe 10 feet by 4 feet wrapping the area where the HWH/washer and dryer sit. I thought I'd take the opportunity to remove the tile. I started chipping the tile off and that was going great but most of the old glue was remaining. Then I started chipping the glue off and realized it would take forever. Next I put a hole in the wall (about a foot square with a hammer and a crow bar. but I'm now afraid I am going to make a bigger mess than I was planning. At one end the tile tile/drywall butts up to a good clean wall I don't want to mess with. Ideally I also only want to remove the drywall which sits behind the tile, not go all the wall up to the ceiling. I do have a recipricating saw (which I have never used) but that seems a little overkill. I can't think of the name of the hand held electical saw wihch you might use to widen cracks in stucco before patching (cost maybe $25). Should I use a small pointed hand saw to cut out the area I want to replace ? Advice appreciated.