I picked one up from Stuart Road allotments. Usually these events have them at venues. Use online map as a "bootstrap".
The map is better on paper - its 2xA5 on a cleverly folded A2. Exercise for reader - how many folds.
There are severe engineering works the last week in October. Southern, Thameslink and Overground. Ian Visits has a clear summary
<https://www.ianvisits.co.uk/articles/substantial-railway-closures-in-south-london-during-the-october-half-term-75505/>