I know it sounds daft, but have you tried your local cobblers? Many of them do other things these days, often key-cutting and engraving. If the latter they will have the shields as blanks.
In our nearest "town" (Newport Pagnell) there is a place that specialises in trophies, plaques etc. Don't think they do mail order, but if you wanted me to enquire and/or get some from them, PM me.