Well, I would doubt someone would make these on account it's more effort than it's worth, however you might be able to do it yourself without having to use a separate program, if you have a picture (made in MS paint) of pretty much a white rectangle, import it into Alice (as a billboard...hehe...get it?). After you've done that, make a 3D text saying whatever you want to put on the billboard, and move it up to the white rectangle. For the pole holding the billboard up, simply use the cylinder shape and rotate it accordingly.
As for a gas tank, I assume you mean large ones that hold reservoirs of oil, you can again use the cylinder tool for the main part, then apply the semi-sphere to each flat side.
Kinda confusing, but I hope I at least helped a little!
