There’s a stall in Robinsons Galleria named Sally’s Kakanin. It’s on the ground floor near KFC and Tokyo Tokyo.
They’ve got Biko, Maja Blanca, Cassava Cake, Sapin Sapin, etc.
You can buy a single serving or you can take out a box of your choice of kakanin.
If my memory serves me right, the latter costs around ₱300.00. A half-box costs around ~₱100.00 or so.