Many motorcycles don't have carb kits available. Kits for cars used to be very common. I've rebuilt hundreds of car carburetors. Probably where I developed my love for them. The only parts I've ever needed for motorcycle carbs were float needles and a couple of diaphragms for the coasting enrichener. Not all motorcycle carbs have those. My former Vulcan 750 had 2, $50 apiece, and ethanol gas destroyed them both. Carbs tend to be bulletproof unless abused. There is nothing in them to wear, other than the float needle. Most carb problems are caused by leaving old gas in them, which plugs everything up. I learned a long time ago to drain the gas out of a carb if I wasn't going to use the vehicle for a week or more.
Any possibility a '96 or newer carb would fit an original Rebel? It's been 33 years since I had my '85, so I have no idea what the carb differences are. I still thing Honda should have brought back the '85-'87 Rebel as it was, other than the headlight.