Baal wrote:
GNER mainline runs through Leeds. Seriously though check out along disused
railway lines - there are often piles of stuff.

Please take care using old timber railway sleepers scavenged from the
railway. They often have noxious chemicals such as tar on them, and you
should note that not all trains have holding tanks for the toilets.
Where do you think that goes?

Also the railway increasingly uses concrete sleepers (or even
occasionally metal) so there will be fewer timber ones to recycle. I
note (from a Balfour Beatty Rail magazine) that old granite ballast is
often classified as restricted (as in polluted) waste, ergo, old timber
sleepers will be also.

I use "gravel boards" in my garden.