A good place to look (
with the help of Google Translate) is
Vereniging Oude Fiets.
From what I know the Gazelle Sport Speciaal is a Dutch only model. While it is true Gazelle made some bike under license for Raleigh (
such as the Raleigh Competition or this Dutch market version of that model) during the height of the bike boom of the 70's.
Where are you located? I know these are rare outside of the Netherlands though there is a very large and enthusiastic following in Indonesia.
Source:
Gazelle Beeldbank