Do you want the tattoo to work with your body (like a design), or is your body simply the vehicle for displaying a picture (like a portrait)?
I'd say you're going to have the best luck in completing your piece by talking with the artist who will be doing your work. Sit down and show him what you like, explain your ideas, and see what s/he comes up with. In my experience, the hardest part of about getting a tattoo is taking the step from the maliable ideas and inspiration to actual artwork, especially if you aren't the one doing the drawing.
In lieu of that, looks through the pictures here. There is a lot of stuff out there, but a vast amount of it has been complied on dieselpunks, thanks to the staff and the forum patrons here :)
I've done my best to collect everything relevant to dieselpunk from the original era right here.
Is there something specific you're looking for?
A leg doesn´t seem like it would leave much room for a propaganda poster thingy. How about an art deco building like the Chrysler building, in silhouette against a dark blue sky, with silhouettes of airships in the sky? If you need something that doesn´t have too much detail, you could look at the Batman The Animated Series cartoon.
The German band Kraftwerk has some imagery you might like. Take for example a look at this single cover:
Then there´s of course the actual propaganda posters:
...oh and man, VNV Nation's website is really Dieselpunk, I never noticed that before I joined this group!
My advice is that whatever the subject it should express something tall, fast, sleek, in motion, or otherwise denote PROGRESS. Look at the vertical and convergent lines of art deco design and how it stresses tall, upward, and imposing, or streamline design (see Norman Bel Geddes) and how even when sitting still the cars/planes/etc. look like they're moving fast. Look at the forced perspective used in the old poster art and how it makes everything seem to be standing tall and majestic above you.
For a leg, I'd go for something vertical like that, such as with background skyscrapers using converging lines to express height, with criss-crossing search lights behind them, of course, and any figure standing magestically "above" (check out the Metropolis movie poster). Something flying in the background, like an airship or retro-futuristic airplane, is another standard icon of the era (make sure it's angled upward, as if it's flying overhead or climbing into the heavens). Use simple straight lines and idealized human figures to express that physical, mental, scientific, and emotional Perfection that's certain to become the norm in The Future.