Morning Mike,
To do this you will need the gear or pulley to also have a morse taper, which if i recall is around 2 degrees. You could have a local engineering company machine this for you, but ensure you get a good finish as this is key to maintaining a good mate between the two parts, a bad fit will result in premature wear.
Another thing would be to use a woodruff key in conjuction with the morse taper.
Not sure if you have an RS catalogue but in these you will find every thing you need, i believe they have a web site where you may find what your looking for.
Paul