Yes , you can get fins that long. I have a 42 in my old mistral race board. Its only rarely used in light wind. I wouldn't want to push off it.
Wonder if a proper glass surfboard fin would be better, like this one. The fin it comes with is very flexible plastic.
I use surfboard fins in all of my boards, sups too. Some surfboard fins are too thick, some are good. I use fins from need essentials which are excellent.
avoid the thin tipped longboard fins. Too much tip flex. Look for the fins with more area in the tip like the image you posted or the whale fin need essentials sell.