Greetings Jan and thanks for photos!
http://www.ribbonsshop.com/ sells a lot of Yugoslav replacement ribbons and sashes, unfortunately not that many for decorations from the socialist era. Maybe you could try contacting them and see if ribbon like that will be available in the future.
PS Just a friendly warning to all of the forum members, there are claims that there are very good fakes of this medal among others. I do not own a piece of my own so I can't say more on this matter or maybe show you some images, but what's indicative to me is that, considering how many of them were actually awarded, they show up too often.