Your plants will stop photosynthesis and not grow at all. What stage of the grow are they in?
I know man. Keeping that temp in check throughout the year is a task. Luckily the temps sit right most of the year here in Wales, in the winter I use an oil heater which works pretty well but I have no control in the summer as I have absolutely no way of getting a fan intake set up. I survived ok last summer but it wasn't as hot as it is now.
Do you have ridge vents in the roof? Gable vents? If so, you can try leaving the door to the attic open and letting the air from the house into it. The heat exiting the ridge vent (if you have one) will suck air from the lower level into the attic and cool it down a bit.
Your buds will finish thin and fluffy. Probably won't be very strong either. You can get an in room air conditioner to help with the heat while you grow. You just vent the air condition into another room or out a vent.
The temp will never go below the temp of the attic though, even with an air conditioner, if I'm correct? I would love to be wrong on this as anything would help right now.
With an air conditioner you can have better control of the room temp. You could insulate the attic and use the air conditioner to keep an average room temp. You could also grow in a basement if you have one. That would be a better place.
D'you recommend any machines in particular?
People have used a chimney as out take but obviously they don't have or use a fire. I'd also imagine a responsible person would fix it properly when done, to not endanger future lives. Multiple in/out tile air vents may be something to look into. Slicing open underside roof materiel to expose tiles/holes may be a last option too. You could also check brick/attic floor height and use air bricks.