JW,
Maybe you could shout out to some fellow 'Bolters in your area to see if anyone has a rivnut tool they may let you borrow???
I couldn't find any FLAPs that rent them as part of their tool rental programs. Harbor Freight has an inexpensive one
https://www.harborfreight.com/45-piece-threaded-insert-riveter-kit-1210.html that comes with some inserts that may make the deal worthwhile.
Just some thoughts.
Dan