I’m told you won’t find them in the US, maybe somewhere online they can be ordered.
Take the joystick to a hardware store like Home Depot or Ace.
Someone there will be able to help you out. If they don’t have the screws, someone there will sure know how to get them.
Do you care if the bolts are as close to stock as possible or do you just need bolts to keep the lid on the stick?
From this thread, looks like M4 hex screws were used. I think you can just use any M4 screw with a square neck.
If you’re looking to go back to stock, there doesn’t seem like much that can be done to replace them back to stock.
M4 hex screws with M3 hex heads. That’s the part that will be difficult to find. MadCatz seems to be the same way.