They are not the same - a Super Porpoise sail should be 85 square feet, a Sunfish sail is 75 square feet.
You can buy a brand new Super Porpoise sail Super Porpoise Sail White but it is pricey.
You might be better off living with the slightly smaller Sunfish sail, you can find a lot of used Sunfish sails, or get the new one for roughly $125 from Intensity Sails.
Had a snark jetwind , same problem. Sunfish upper and lower spars are the same. Jetwind had an extension on the upper. Removed it added intensity sail. It's awesome. Option 2 Suoersails.com in FL. Call and get a quote. Est 300$ high quality
I had a Super Porpoise that I sailed on Crystal Lake, Michigan back in the day and I eventually replaced the original SP sail with an aftermarket Sunfish sail and the aftermarket sail worked fine. The Intensity aftermarket Sunfish sails are race cut and have plenty of power so even if they are somewhat smaller than the SP factory issue sail, they should work fine. You can buy an Intensity white or Red-White-Blue sail with a window for under $150.
I have a good inventory of used aluminum Sunfish spars (masts & booms) and also have a set of used Super Porpoise booms in the collection. Do you need either an upper or lower boom for your boat? They are hard to come by as they are a little longer than Sunfish booms and are no longer being made for the SP. I would sell them for $40 each; $74 for both. If you are interested, let me know. I live in Cazenovia and could meet you halfway between Cazenovia and Canandaigua to deliver.