Most hotel provide wedding ang bao boxes as part of their wedding banquet packages. If yours does not provide, you should demand two from them. Alternatively, if you prefer to get one yourself, you can consider searching online, there are many online shops in Singapore that selling wedding favors along with Wedding Ang Bao boxes. Prices range from $30 to $50 per box.
If that is too expensive for you for a simple box with some wrapping paper on it, you can consider DIY one yourself. Honestly it is not that difficult, just got art shops to buy boxes and some wrapping paper and you have yourself a Wedding Ang Bao box for less than $10.00. To beautify that box, you can consider buying a ribbon to tie across the box as well.