Dumb question - how to find gravel (rides)

Depends where you live. There isn’t much of the US-type gravel in the UK, for example there are very few gravel roads. Often re-purposed old railway lines can be good, or in the NE there are more off road roads. Scotland too maybe. Otherwise, farm tracks and fire roads in large wooded areas. Most of it though will either be compacted soil (gravel long gone), tarmac, or, in the hills, very rough gravel that is probably better on a MTB.