“flux capacitor”
Really exist. If that was the only requirement, I could furnish one. (note, they have nothing to do with time travel)
A flux capacitor is easy to get. Granger probably has them on the shelf.
The problem is getting the plutonium to generate the 1.21 gigawatts of electricity. Also, the speed limit is about 60 mph. You need an open place so you can get that sumbitch up to 88 miles per hour. You could get a ticket for that.