2008 Toyota Camry accessory hookup

I purchased a back-up sensor kit for this car. It has 2 sensors in front and four in back. The back hooks up to the backup lights. My problem is this. The system needs an accessory hook-up to power the display and front sensors. However when looking for a power supply, both fuse boxes have no extra accessory slot for additions. Where would you tie in the system on the acc. Side? I dont want to tie in to just anything because of the computers. Can you help?