Hex,
This was your question:
"...Question: How did you go about finding a sponsoring local firm?..."
The answer is: The sponsoring firm (of your EP) has to be set up first. You can only do that with the help of a local company that will provide you a local director (hence the link I provided earlier). A representative office is a very limited type of entity. See this link for details:
http://www.business.gov.sg/EN/StartingUp/ForeignBusinesses/If it is an EP you seek, it may be better to set up a Private Limited Company instead.