yes,
most metal supply facilities offer up to 240" long and 120" wide. for your boat, I think a 72 x 144 would be fine. start looking on google. your looking for companies like Alro, or American Metal Supply, or Ryerson or what ever metal supply facility is near you. They can advise on what they have in stock, or what they can get for lengths
if you have to form anything, stay with 5052, forming 5086 requires a 3T bend radius where 5052 can use down to 1/2T
be prepared, aluminum sheet is about $3 per pound, and a sheet of 11 gauge in 72 x 144 will be close to $400