Phonics dice can be bought online from some educational retailers but printable dice (cube) nets are also easily found online and are much cheaper. Dice with plastic pockets are a really useful classroom resource as the teacher is able to change the sounds or words whenever needed. They can also be used for maths and even to make song/story dice.
Differentiation within the same group of children can be achieved through having multiple dice. One die may have more advanced sounds or even words.
Alternatively multiple dice could be used to make words with one dice having only vowels and others with consonants.
Resources: Printable cube nets / plastic pockets / phonics flashcards