Howzit! its quite tricky trying to find suspension for a Sirion but there are some companies that do it!!!
Go to www.d-sport.web.com and go to the Daihatsu Boon (name in Japan for Sirion!!!) you will find wat you are looking for!!
Another option is to got to the Toyota Racing Devolpment site @ www.toyota-trd.com and look in their catalog for Toyota Passo (same as the the Sirion, just got a toyota badge!!) you should find springs + some other interesting parts!! I hope this helps...

Anyways drive fast, stay safe!!