You can get ectaco jetbook, eco reader, iriver story or oaxis ebook reader at iknow stores around the island. They might be limited in stocks at certain outlets, you should check before heading down to take a look/buy. Their website ->
www.iknow.com.sg
ebookshop.com.sg has a few different selections like hanvon, hanlin, cooler and etc. But i don't think they have physical outlets like iknow. There's a shop in Sim Lim Square that sells imported kindle and a shop that also sells foxit eslick reader.