I wanted to select 300 users at random from a row of 10,000 users in Excel. Really easy, but a bit of a lateral solution: Rather than trying to randomly select each item, just order them randomly instead:

1. In another column adjacent to the column of user names, create a random number for each row (the formula I used was =RANDBETWEEN(1, 90000)). This won’t guarantee unique values for each item, but it doesn’t matter.
2. Copy the the column with the formulas and Paste As… Values to another adjacent column. This fixes the nubmers and stops them from updating.
3. Sort by this third column and take x users from the top. I chose the first 300.
4. Done