You can't buy the template seperately, only as part of the armrest kit.... which also includes an armrest!
I fitted my armrest a few months ago and it was quite a scary time, cutting through my centre console. Although looking back it's quite simple. You have got quite a lot of room for error as the armrest trim covers almost all of the possible area you can cut the hole.
To help, once the armrest is fitted the measurements are as follows.....
From the top edge of the rear ashtray to the back of the armrest trim is about 7mm. And from the storage area to the front of the armrest trim is about 10mm.
From those measurements you should be able to work backwards to calculate where the hole needs to be cut.
The width of the hole is easy, just make it as wide as the hole for your storage area, maybe a little narrower.
As for actually cutting the hole, the plastic is pretty soft. I drew with a pencil the place that I was going to cut the hole, drilled a few small holes in each corner using an electric screwdriver with a drill fitting in it, then used the blade of a hacksaw to saw from corner to corner.
You will need a bolt
and a nut to fix the armrest to the car. I used a 25mm M8 nut and bolt. 50mm was too long.
There is a hole in the bracket that the armrest fixes too but there is no thread in it. It's just a hexagonal hole.
I found inserting the bolt from the bottom and screwing the nut on the top side was easiest.
Here's a pic to show roughly where I cut the hole (red), and where the armrest trim sits (green).