Not sure if everyone knows this already, but if you badly need a Support Unit refresh and you’ve used up all 10, a cheap way to refresh it is by attempting easy missions (like 1-7), use a support unit, then once the mission starts, EXIT. You can try any mission (that isn’t challenge mode), but I choose 1-7 in case people want to farm orirock cubes anyway.
Essentially, you’ll be paying 1 sanity for every refresh once you used up all your Support refreshes.
Hope this helps someone out.
EDIT: If you’re also kinda desperate to use that one unit you need, just browse through your friends list, list down the people with the key operators, and delete the others. Just add them all later if you want.
Better, just delete everyone else except that one or two player with the operators you always use. You can always just add the others back.