Amongst my poking around today I found that Tein makes a coilover kit and a spring kit for the Mirage!
Spring kit: SKE46-G1B00
Coilover kit: GSE46-11AS2
Here is a PDF that shows images and specs of the spring kit:
I then googled the part number for the spring kit and found a Japanese Amazon page selling the spring kit for 17,157 yen. You'll have to convert to your own currency to get an idea of what that is, but that price seems quite reasonable.
The coilovers I also found on a Japanese Amazon page. They are much more expensive at 74,240 yen.
However, I would imagine you could call up your local (or at least in your country) Tein dealer/distributor and give them the part numbers. They should be able to get you a price. I don't think it would be horribly hard to get these parts to you since you know the part numbers now.