Thanks guys, the ones I saw advertised at various online stores in the US and the UK and on gbase were all far more expensive than this one, which seems to be unmolested and original.
AFAIK "walnut" was not a colour option for the Triumph, so it must just be a natural 'hog finish that has had a good life!
Iome, thanks for the reassurance about the seller. He responded quickly to emails, and his listings and feedback all look great, so I figured he would be a safe bet to purchase from.