Try calling the bass gallery in camden, they tend to stock Labellas.
www.thebassgallery.com
It's also worth looking at
www.thomann.de - granted, they're in Germany, but their site is available in English, prices can be displayed in pounds, they're UK VAT registered, so really there's very little difference ordering from them vs. any UK based mail order firm.
I don't find their site very easy to browse, though, best to just search for Labella.
Cheers,
Nick