If you are refering to company's financial reports and offerings, the required source for companies to disclose the information is the SGX website (www.sgx.com) under the Company Disclosure tab.
This includes annual statements for the last 5 years, prospectus for any shares/debentures/buy back/etc which is being offered, IPO offers and shareholders meetings.
You may also find it useful to check the Research section of the SGX website where some of the public listed companies have voluntarily allowed independent research firms to monitor their company for a couple of years and produce a research report.
If you are referring to filings under the Companies Act, these can be found at the Accounting and Regulatory Authority (ACRA) website (www.acra.gov.sg) and you can also purchase extracts of specific filings under the ACRA iShop.
To understand the Singapore public listing system and the steps to public listing, you may find it useful to purchase one of the resource documents available for Singapore law, finance, tax and corporate secretaryship which are sold by CCH (www.cch.com.sg). Specifically for public listing the Singapore Annotated Listing Manual may help.
It is common practice for companies here to employ law firms and research firms to do the majority of this research instead of doing it themselves which I one of the reasons this information is online but perhaps not so visible.
I hope I have understood your question correctly!
