Your name looks likes Dutch or Belgium. In that case it is easy to provide. I have bought the filter at Conrad.nl (also well known in Germany). The filter is made by Schaffner art. code FN 2020-3-06.
You can order it also by Conrad.nl link https://www.conrad.nl/nl/ontstoringsfil ... 98713.html
It is original made for 230 Volt. But it can be placed also in the 12 Volt supply of the LaCie. It is very easy to do. You have to cut the original supply line and place the filter in between. Be secure that the + line is later on the same place of the connector put into the LaCIe. E.g. the + voltage is the innerside of the connector and therefore the - voltage on the outerside. Important is that the earth (ground) of the filter is connected to your earth/ground wiring of your living!
If you have still questions, please reply.