AFAIK, there are no readily available 5V sources. There must be a 5V PWM controller in the dash pod assembly, as most gauge systems operate at a regulated 5V (otherwise the instruments would vary as system voltage goes up and down). But I don't know where you could tap in. For the same reason, there would probably be one internal to the EDS computer (when you install your Diesel and discard the gasoline ECU). Again, no way to tap in. It would be easier to build one, or just hardwire a USB phone charger, which are widely available. If you will be using it to charge an Iphone, you will need more than a 5V source anyway: Iphones also require 2.8V and 2.0v sources to charge correctly. Dashcams should have a 12V interface, unless you plan on building one from scratch.

Think about something like this, which can be tucked away unobtrusively:

https://www.amazon.com/Cllena-TOYOTA-Dashboard-Charger-1-2A-2/dp/B01CTOKI06/ref=sr_1_2?ie=UTF8&qid=1469792720&sr=8-2&keywords=dashboard++usb+socket+12v+dual