How can I create a list of numbers in a combobox?

I have a client who has asked for a number of dropdowns in their form which can be any value between 1 and 240 months. I assume there must be an easier way to set this up than typing the numbers 1 - 240 multiple times?

Alteatively - in fact preferably - is there a better control to use for this than a combobox? It seems to me that scrolling down a list of 240 items is not a very good user experience.