You can book the london cab online...
Many colors available, rates and details are on the website. Fill the form in and someone will call you back.
http://www.smrttaxis.com.sg/website/2/Wedding/booking_rates.html
Just bought mine from Kalms, with slit on top.
$18 for big one, $15 for small.
Colors: Copper, Gold, Red
You can buy ribbons from them and they will tie for you, but no flowers...