I'm fairly certain that for the Quantities symbology, you must have a field that is a numeric type, that is to say Short Integer, Long Integer, Float or Double. I'm guessing you are using a text field, which won't show up as a possible selection for the quantities symbology. If all your data in your text field is numbers, then you should be able to make a new numeric field and set that field equal to the text field and symboloize off that field.
Either that or if the field is a joined field, it will not show up, you need to make a new field and copy the values of the joined field to it.