The iRobot Roomba 980  comes with one spare side brush. I have to change to the spare side brush after one of the brush head of the original broke.
After changing to the spare side brush and scheduling it to clean just once, all the three brush heads broke. It is probably due to hardening of the rubber of the brush head that makes it so brittle.
Sadly, the only way to get the side brush is from the official agent of iRobot products in Singapore, John Ackerman. Their address is Blk 34 Upper Cross Street, #04-138 Singapore 050034.
Because there are so many parallel importers of Roomba in Singapore, you need to prove that you bought your Roomba from John Ackerman before you are allowed to purchase any accessories. I don’t have a problem with this as I got mine from John Ackerman. Nevertheless, I find this requirement ridiculous.
The iRobot Roomba Series Side Brush  retails for S$30 and comes in a pack of three.
Delivery fees charged by John Ackerman is ridiculously priced at S$20. So I went down to the shop to buy it instead. Their opening hours are from 9:30 am to 6 pm on weekdays and Saturday is from 9:30 am till 1 pm.