These wonderful cards by Georgie Birkett were bought quite some time back at Tom & Stephanie. Sadly, I don't see this there anymore. Fishpond.sg once carried them as well, not sure about now.
Budsy bought both the Small Alphabets version to teach both chubs and dragon_boi the letters of the alphabets, used Montessori sandpaper letter cards to teach letter sounds and the numbers version of Georgie Birkett's Count With Me board-type cards to teach the boys their numbers.
If you're looking for alternatives to Montessori's sandpaper letters and numerals, you may consider this range from Georgie Birkett.