You can sell your good jokes to all kinds of comedian and cartoonists if you follow simple procedures when submitting. But like Greeting Card writing, this is an extremely competitive field and unless you are very good, you cannot expect to make a living at it.
Start by looking through the latest edition of the Writer's Market under Gag Writing. You might be surprised at the large number of cartoonists looking for work, and even more surprised by the kind of work they're seeking. Make a study of this section of the book before you start writing gags and making submissions.
One idea: when making your first set of submissions, include a card that reads as follows:
Thank you for the submission, but I am returning them because they are:
___ Not suitable for my markets
___ Not professional
___ Not funny enough
___ Not funny at all
___ I don't need new submissions at this time
Expect to see the last slot checked off frequently. What this card will do is show you who is most impressed by your work and who might be a better bet for a future sale. If you sent your best batch of gags to someone you thought could use them and he says they aren't funny at all, why waste postage trying to change his mind?
If you want to give this a try, start writing gags immediately and file a lot of them, several hundred if possible, before making your submissions. The more you have to choose from, the better your choices will be and the better your chances of making a sale. Be aware that payment for cartoon ideas is not as good as for greeting cards.
If you get some positive response from your submissions, you might even want to start hanging around at comedy dubs. Young comics need the very best material that they can get if they hope to make any sort of name for themselves, and many will be happy to pay two to five dollars for a good line. Provided, of course, that you don't turn around and resell it to someone else the next day.
Don't forget that many daily newspapers and magazines pay cash for good jokes but they tend to get swamped with submissions, so unless you have a lot of faith in your idea you just might be wasting postage.