After his retirement from comic book work in 1966 Carl Barks was asked several times by the Danish worldwide distributor of Disney comic books, Egmont Publishing, if he would consider making more duck stories, but he declined every time. You can see an example of the correspondence HERE. The editor-in-chief, Carsten Jacobsen, had had more luck persuading Barks to deliver new material on an earlier occasion as you can see HERE (second paragraph), but this was the last time he agreed to dream up a Scrooge story.
Barks softened up quite a bit in the first half of the 1970s, though, when he churned out no less than 24 full scripts and rough sketches for Western Publishing's new HDL-magazine containing stories about the Junior Woodchucks (see them HERE), and apparently Egmont got a new chance to do business with Barks. He not only agreed to write a short synopsis for a Gyro Gearloose story, he ended up sending them a full descriptive script (i.e. no finished dialogue)! The script was never used for a published story, and it is presented here for the first time. The reason for the story to be rejected is anybody's guess...

Initially, it would seem that Egmont approached Barks via the Disney Company as this original letter suggests:

For unknown reasons Barks was suddenly - and surprisingly - interested in scripting a new story, and within three weeks he was able to send a letter, which he forwarded to Carsten Jacobsen personally (the following is Barks' draft):