Thanks for everyone's advice, I've vetted them all and thay all look great in different ways. It's amazing that such a needed item isn't readily available, particularly from places like Ultimarc etc.
For everyone else's sake - andysarcade do 'conjoined' clips that fit on many generic UK cocktails. Unfortunately these don't work with my design, where I have large radius rounded corners.
Arcade Depot US supply them and will ship to the UK, on request for a slightly higher postage charge.
The spacies ones look absolutely fantastic, and I would highly recommend them to anyone building a 'keeper' for themselves. However I am looking at a cost-effective solution 'off-the-shelf' for a friend's cabinet.
Thanks for the pointers guys.