You need to be disciplined, get up early and go the newsagents as soon as they open. If they normally stock them, that should do the trick.
Would have thought the big days would be less of a problem, 4 or 5 copies on Derby Day compared to 1 this week.
I used to leave it occasionally to later in the morning and sometimes struggled but never failed to get one.
Supermarkets and petrol stations usually have one.