pretty sure they stopped selling them in the early eighties it coincided with a 20% -30% drop in the collectable coin market at a guess 1981 or 1982.
They have never been for sale except in the second hand market since.
In the mid to late seventies whitman folders retailed around 25p to 50p range its now virtually impossible to get them for less than a £5 note.
On their own they have been a great investment