Depends on the Classic. For an MG or Triumph, there's not much that can't be on your doorstep the next day. Same day, for me, but I'm lucky to live in the home of Victoria British.
BMWs aren't far behind. They've done a stellar job of supporting their older cars.
Other cars can be tricky, particularly if they're an orphan. Some classics definitely have difficult or non-existent parts supplies. I'd be wary of using one of them as a DD.
Oddly, it seems a lot of 15-20 year old cars have iffier parts availability than older classics.






