Sorry but I do not remember who was selling the complete mirrors with the in-built indicators or even if they were for an LS400. They might have been for an LS430 or GS. There is an old, lengthy thread on clublexus.com about signal mirrors -- the thread may have links to sellors. I have also seen at least one post on clublexus.com about adapting Mercedes mirrors for use on Lexus cars. All these options were very expensive.
Doesn't your U.K. spec LS400 have side mounted indicators or is it an "import". It is very easy to add side turn signals to cars that do not already have them. I bought OEM side turn signals and the required repair harness from a U.K. dealer shortly after I bought my first LS in 1990. I had them professional installed by a body shop - total cost was probably less than $150.
Yes it does I have just changed the side repeaters to clear from orange to match the front clear indicators,makes a big improvement in looks.
It was just that if I could have got some decent signal mirrors at a decent price I would have liked them but its not the end of the world.
I would rather go without than have something that does not look right.