I'd ask around and see if anyone has one they will loan/rent you. Like Bio said, youre probably going to have a tough time finding someone to work on this, but you might give some of the commercial refrigeration guys a call (think people who fix HEBs refrigerators) to see if they can help you or point you to someone who can. In any event, if it's 81 at night, I'd crank the house AC down to try and mitigate this as best as you can (I'm talking like 72) and see if that gets you where you need to be. If not, you can turn the lights off until you can get a loaner or replacement chiller. If they're not already employing evaporative cooling, you can put a box fan to blow over the sump, and that should keep you in the low 80's as well, you'll just need to keep an eye on topoff water. I'd guess that all of the LFSs have 1/4 HP chillers in stock, so you might put a feeler out to the GF's parents and let them know that it might be a good time to think about replacing the non-functioning chiller.