Most big box stores will sell the stepped adaptors for shop vac hoses. I bought the one I use from Home Depot. I use a 1.25 inch vacuum hose for my bench sander, small lathe and drill press. For some reason the bench sanders vacuum dust ports are slightly larger than the end of the 1.25 inch shop vac hose. So I bought the stepped adaptor, cut off the part that fits the 1.25 inch hose and use that on the end of the hose so it will fit into the bench sander dust port.
Or, if you have some PVC pipe or PVC fittings laying around, and you have a heat gun, you might be able to make one yourself. I did this for a few things around my shop. I made a few fittings for my 2.25 inch shop vac hose so that it will fit onto my dust collection system I made from PVC pipe.
It is amazing how much the PVC pipes/fittings will expand and take the shape of just about anything you place it over once you heat up the PVC enough to make it a bit mushy!
I use the heat gun so that I don't burn the PVC or leave scorch marks on it that you can get from using a torch. It takes a few minutes longer with the heat gun, but it works fine.
Here is the stepped adaptor I bought from Home Depot.
Jim