The trimmings are not a major part of this dress but are nonetheless important. I found it surprisingly difficult to find a square diamonte buckle, they were nearly all rectangular! I did find these shell buckle ornaments (see far right) which I felt I could change into dress clips for the shoulders.
I couldn't find any belt buckles in haberdashery shops so decided to look in some antique and second-hand shops. I found this lovely belt buckle (far left) which I believe may well date to the 1930s due to the art deco-esque shapes. Whilst it was a different shape from the buckle in the design, it felt more elegant than the squarer buckles I'd found and suited the dress a lot. There was one problem: the vintage buckle was startlingly different in tone from the new shell ones I'd bought previously! I was first a little concerned as all the dealers told me that there was no way of polishing up the vintage buckle, and I didn't really want to break down the new ones too much with French Enamel Varnish as I didn't want to spoil them.
Further searching however led me to find some real dress clips, also seeming to be possibly from the 1930s or 1940s. The trimmings are slightly tarnished and missing a few stones but overall I feel that they add to the period look and feel of the dress, and the age of the buckles, and quality and colour of their metals, look very nice with the colour of the dress.
In industry this method of sourcing, of course, might not always be suitable. Trimmings from an established supplier might be requisite so that they can easily be re-ordered and/or replaced in the future.