>>1863134>find boomer markets where they don't know what they have and check dailyThis.
Also local classified ads, gumtree and similar, house clearance sales can be a rich vein, I have a deal with a couple of local house clearance contractors who send me pics of any bikes that turn up, they know if I'm interested then it's worth at least something, so you know, in order to keep the pipeline open you have to pay a fair price (for them), but it's still going to be a lot cheaper than buying from someone who knows exactly what they have.
I picked up picrel for £35, that baby may have been filthy but it was decked in barely ridden M900 XTR, once cleaned up I was able to sell the group for £1000. The frame, a Roberts White Spider, I kept because barely ridden Columbus steel built by a master doesn't fall into your lap every day, but has a potential market value of £500 - £800.
There be treasure out there.