Hope you didn’t pay too much for it
This is a tricky topic to help with for one main reason, Mods, if you have any knowledge of any mods done to this quad such as, resurfaced head, bored to a bigger piston, etc. please list those first. If you are not sure please contact who you purchased or acquired the quad from and please find out for us. This will help us get you correct jetting for your carb.
Please start by measuring in MM the inside diameter of the carb opening on the engines head. Most common sizes are 26MM to 38MM to my knowledge, but this size will help us get you a carburetor.
I will also provide links to carbs, please do not buy cheap eBay carbs, this would not be good.
Exhaust kits can be purchased on any aftermarket parts distribution website. If you need any help with that I will provide a few links as well.
We’ll get to your clutch and brakes, once the listed above is completed because that’ll take some time