Hi,
Unless Eldis can help, your best chance is to duplicate the decals at one of the "vinyl van lettering" places. As well as doing "Bob the Builder" in self sticking vinyl, they can do all sorts of shapes, lines and patterns - and just like a decal they are removable.
Some of our Eriba owners with 40+ year old vans have no chance of getting original decals, so the vinyl shop is a good route.
Alternatively, use the edge of the existing decal to lay down an outline in masking tape, remove the decal if it's in bad condition, mask off the surrounding area and buy a can of matching car spray paint - but only if you have some (good) experience of using a spray can.
Or if you've ever travelled on London underground, the guy that tagged most of the bridges and trains with the logo "TOX-04" is probably out now and you could commission him to do a custom paint job for you :-}
Robert