Greg, I had the same problem. I contacted Bing for parts. Most are available but just for a new slide was around $160.00 !! I bought a mikuni for $100.00. It takes some work to fit it but they say its worth it. I haven't ridden mine yet.
I bought mine on ebay, it was 104.00 and they also had them prejetted for a little more. I just searched penton in ebay motors. I bought mine from weekend warriors, but I think there are others. Just look at the feedback and buy from a reputable seller.Also search here for mikuni carbs and you will find some info on fitting them.You will have to modify the air boot and the intake mounting. I used a 2 inch to 3 inch fernco fitting and modified my airboot. I shortened the carb by cutting the rear bell and I cut the intake manifold a little too.The mikuni is a little longer than the bing.Good luck, they say its worth it.