your best bet would be to try to rent time on one in a local fab shop, doubt you could rent one, get a new one on approval, test it and send it back! 4mm, needs to be a big one...
As above - either ask if you can pay for time at a local fab shop (between covid and H&S this is pretty unlikely...)
or maybe pop your head in the door and offer one of the guys a bit of cash to cut everything dead on for you on his lunchbreak. I know I’d happily cut a heap of stuff for someone for a £20 note and a bacon roll
I have no sheet metal tools, so on the odd occasion I need something cutting I co to my local stair and gate fabricator, the owner will always do small jobs quite reasonably