Obtaining a Switch on older firmware requires purchasing a Switch that has been in stock in a store for a long period of time. This is true in all areas of the world. For this reason, populated cities and well visited stores very unlikely have any. Try rural areas or small electronics stores/supermarkets.
Review the serials in this thread and compare them with what you find on the box.
https://gbatemp.net/threads/switch-firmware-by-serial-number.481215/
While you're there, leave the first 9 characters of your serial there and your firmware.
Especially if it's
above 3.0.0, doubly so if it's 5.0.0. Knowing which serials to avoid helps future buyers.
Here's a reference chart of all the data we've collected so far: