The aftermarket pipes are very hard to find, I tried for over a year and just gave up.
There are ways to make the stock system louder if you want to. You can remove the mufflers, if you do I’d put some exhaust tips on the pipes just to move the sound back because without the mufflers the output is directly under your head and can be very droning at highway speed.
Option 2 is to gut the mufflers and remove the baffles, labor intensive but gives the bike a deeper type of sound. This is how I’m set up today.
Option 3, remove the goats belly, I’ve seen folks put the mufflers directly on the headers, use HD mufflers, and just flat out leave everything off, this is as loud as you probably could get without some kind of megaphone exhaust but like I mentioned above this will be right underneath you,
except for gutting the mufflers, everything is reversible if you don’t like it, I gutted the mufflers because they were broken already and I figured I couldn’t make it worse.