I think you're going to have a difficult time finding an acrylic sheet at that size unless you're near a major metro area. And even if/when you do, the shipping costs are going to be high. After that, you're going to need to consider how you're going to unload it from the shipper's vehicle, how you'll be processing it, etc. I'm not saying you won't find one, I'm just opining it's going to be a major P.I.T.A.
I'd also suggest looking into polycarbonate as an alternative, as it could be rolled- meaning less cost for shipping. I personally don't care for using rolled poly because- depending on how long it's rolled up- it will often want to stay rolled. Then again, poly will be more durable and, in a sheet that size, that would more than likely be a major consideration.
