Chris:
There's always Kinko's or another office supply shop wherein you can try Robert's method...
For going the custom graphics route try looking in the yellow pages under 'custom photograpy', or 'custom graphics', or 'drafting contractors'. If you bring your original images to them, along with the decal paper, they can probably help you out.
It could end up being quite expensive so I recommend talking to them extensively about what it is you want, and maybe see if they'll do a sample or trial run.
Good luck!
Bruce
PS:
These shops can usually do PE positives as well.