Here are some simple dice rules to allow you to simulate the distribution of the damage A deck if you don't have the cards.
Use 2 d6 of different colors.
The first color is the positive number. The second color is the negative number.
When rolling the dice, take the positive number and then subtract the negative number. If the sum is positive it will be a number between 1 and 5. This is the damage. If the number is zero or negative then it is a miss.
For example, the first die is rolled with a 5. The second die is rolled with a 1. 5-1 is 4 damage.
Another example - The first die is a 3, the second die is a 4. The result is 3-4 = -1 which is a miss.
This will distribute the damage roughly to the same weight that the damage cards do, with a lot of misses and then fewer of the higher numbers.
An optional rule - If you roll doubles then your guns are jammed.
Richard Bliss