Well, it was a matter of time but here they are...
http://www.ebay.nl/itm/Replacement-Silicagel-Fast-Install-Band-Watch-Strap-For-Garmin-Fenix-5-GPS-Watch-/201935426415?var=&hash=item2f044a136f:m:mCIkDLhdVYOlP22GiET-aOw
I ordered 2 to give them a try (blue and yellow). After ordering the official black and leather one (which still isn't delivered) I couldn't make myself spend another 100 euros for another 2.
10 euros is more like it (***, if the official ones were around 30 it would already be less of an issue). Anyway, just in case anyone wants to give it a shot ;)