A question about A Late Message From Avalon
After my third rewatch, I still have one question. Where did "Arthur" get his sword and chain mail?
It's a good episode, and this question doesn't detract from that.
You can easily buy that stuff today. In the future it's probably even easier.
Bought as a costume? It's a plot hole, you're right.
I don't see it as much of a plot hole; I'd assumed he'd previously had an interest and had some replica stuff lying around (as people do today) and so when he needed an escape he had them to hand for his fantasy/delusion.