How do I export visiting cards onto one page?

I have a script to generate visiting cards for the entire team from an svg template. It spits out a single pdf the size of a visiting card, like so:

+-----------------+
|      o  o       |
|      \__/       |
|                 |
+-----------------+

Now, for printing, I know 12 of these fit on one A4 page. If arranged like this:

+---+---+---+---+
|   |   |   |   |
|:) |:) |:) |:) |
|   |   |   |   |
+---+---+---+---+
|   |   |   |   |
|:) |:) |:) |:) |
|   |   |   |   |
+---+---+---+---+
|   |   |   |   |
|:) |:) |:) |:) |
|   |   |   |   |
+---+---+---+---+

So, I need a script to do this on the pdf level. Any clues what tools might do the trick?