Mother of Groom non- high street suggestions please?

Can anyone suggest any online or independent shops to look for a MOG dress without looking like something out of Dallas or Dynasty? It's going to be a top end wedding at a posh venue in Spring so I don't really want to go high street if at all possible in case someone else has the same outfit. I've looked online at the likes of Nigel Rayment but they seem very expensive and I'm not sure the quality would be worth it? I'd be happy to look around Bristol/Bath/Gloucester/ Cheltenham area maybe even London if I had to or online even better. Any suggestions out there? Thanks.