If you haven't already tried a local dealership's Parts Department, you might have success at
Texas Toyota of Grapevine. That's where I got mine after my dealership told me they had no clue

. If you don't find it listed on the site, leave a message under Contact Us or call the number there and ask for Kevin

in Wholesale.
Since it's the same
running boards, Sequoia, rather than Tundra-specific installation instructions may be included in the box. If so, you can access instructions for the Tundra from the
TS Knowledge Base (must be a subscriber to access).
The electrical connection is T-tapped off the wires to the underdash "step light" between the steering column and driver's door. The RB lights then follow the interior lights, including fade-to-off. Post back once you've got the boards and I'll give you a few more tips.