Megan Racing and Motordyne are typically the go-to aftermarket pre-made exhaust pipes.
Or you can easily get custom work done for the same price or less. Buy some v-band clamps off ebay if you go custom so you have a way to easily remove the exhaust instead of just welding it all one piece.
V engines like we have gain horsepower from Y, H, and X pipes. It needs the crossover so suction from exhaust gases pulsing by from one bank can act on the other band to draw in more air into the cylinder. X pipe gains the most performance though because the way it crosses over has the lowest resistance and change in direction of the exhaust gasses. If you go custom, you may want to go with an X instead of a Y. They are pretty cheap on amazon.