Sorry, but there will not be any more icons added (unless there will be some more standard allergens commonly listed by the WHO or similar)
First of all, because everybody will want some others/more
Secondly, using/adding icons and distributing them will – in most cases – require a license (i.e payment)

In short:
You need to add your “Frozen” to the list of “Food Types” and the use css to add the/an icon yourself (i would suggest you use your browsers element inspector to see how its done for the exiting icons and adapt your css as required)