Short answer: Search for “Philips TV Remote” on eBay
Longer answer: As you can read here the startmodule can be put into a specific mode where it will react on a normal TV remote instead of the referee remote. Pressing channel 1 on the TV remote acts as a start signal and channel 2 as stop signal.
This is a useful feature when testing your robot at home. You can try with the remote you have at home however if it doesn’t work it might be because it uses a different protocol (for example NEC) instead of the Philips (RC-5) protocol. If you search for Philips TV remote on eBay you will find a lot of options for just a few $. If you have bought one that you are happy with please leave a comment with a link for others.