This is simply never done, and for very good reasons. With the advent of digital typesetters and digital fonts, it suddenly became possible to create a fake-italic version of a font by slanting the letters. The standard slant that I am familiar with is 12 degrees, but of course with digital fonts the letters can be slanted to whatever degree you want.
But what usually happens is that the font looks like exactly what it is: roman font characters that have been slanted, and therefore distorted. Round characters look strangely squashed. Slanted lines are suddenly uncomplementary widths depending on which way they slant. Slanting a roman to create fake italics does violence to the letterforms.
Another problem with slanting roman characters to create fake italics is that an italic version of a font usually has at least several, and often many, characters (often including “a”, “n”, and “u”, to name just three) that are completely different from the roman version of the font. This applies more to serif fonts, however; many sans-serif fonts do not exhibit these differences—and their slanted versions are therefore called “oblique” rather than “italic”. But even an oblique version cannot be simply slanted without distorting the letterforms in an unattractive way.
Nevertheless, I wanted to get an idea of what a Jetsonville Oblique would look like. So I slanted the letterforms (most of them, anyway) 12 degrees and saved the characters as a new version of Jetsonville. Looking at it, I see distortion problems—but they are less objectionable than I thought they would be. I can offer a possible reason for this: The design of Jetsonville is already so quirky and eccentric that the distortions introduced by slanting the letterforms are not as noticeable as they would be on a “normally” designed font.
I did not slant all the characters in the unofficial Jetsonville Oblique because there are certain characters that, even in an italic font, are not slanted. Slanted © and ® characters, for example, would look strange and awful, so even in an italic font they are left as roman characters.
Up to now only one other person besides the font’s creator has seen this version of Jetsonville, and he did not see the entire character set. But his comment on it (“That, my friend, is pretty tasty”) encouraged me to go ahead and create the entire Jetsonville Oblique font as a further trial balloon.
Enough explanation—shown below is the unofficial Jetsonville Oblique.
