When the meaning is "to have an amount that is less, by some amount, than a required amount" it is idiomatic not to use of but to say
I'm short ten dollars. I need to visit the ATM.
short + shortage-amount
You need ten dollars more in order to reach the amount needed.
When the meaning is "not reaching a number, less than" then you find of:
The population of the district is short of 10,000.
The tallest building in that city was short of 100 storeys.
The population might be 9,873 and the building could be, say, 97 storeys high. The implication is that the number is approaching the specified number.