Buy foreign cash for delivery

I like to take some cash with me when I travel, but I’ve been caught out in the past when either Revolut is offline or I can’t find a local ATM as I arrive somewhere.

At the moment the only way around that problem is to order cash from someone else (at a considerably worse rate) before I go. For example, at the moment I’m looking for Norwegian Krone and the best online rates would give me between 100 and 150 less Krone for the same amount of Sterling when compared with Revolut.