You might not know this or believe this, but many comedians buy the jokes they tell. Most of these comedians rely on freelance joke writers to keep their material fresh, even if they routinely work with a specific writer or group of writers. The only way to know if a comedian is interested in your jokes is to get them out there and on the joke market.
If you're going to sell jokes, you're going to have to get down and dirty and work your local comedy clubs. This might be the most important step in this article and it will benefit you in two ways...
1) You can test out the material you're planning on selling to a live audience. You can write all you want, but unless you try your bits and routines in front of a live audience, you'll never know if your jokes really work.
2) Depending on how popular your local comedy club is, it's very likely that well-known comics are going to play your local club. This is where you're going to network and develop with relationships with nationally touring standups. Depending on the celebrity comics that you meet at the club, pitch them with the idea of selling them jokes. When bigger comics are developing new routines, it's very common for them to use a team of writers and freelance joke writers.
Know your audience, or in this case, the comedian you want to write for. If you're going to pitch someone like Billy Crystal or Robin Williams, you can assume their jokes are going to be very topical and inoffensive. Now if you're pitching jokes to a Chris Rock or a Dave Chapelle (yes, they use writers every now and then), you can go topical, but you can also get a little raunchy.
Look into television. Shows like The Tonight Show, the Late Show and the other numerous on late night television already have teams of top-notch writers, but you can always write to the show and ask if you can pitch them jokes and skits. At this point, you'll probably be asked if you have an agent or manager. That's where the next step comes in handy...
If you're serious about the selling of your material, get an agent or a manager. Anyone who will protect you and your original jokes. These are the people who are going to take about 10 percent of your earnings to protect you from other comedians from stealing your material and also get you gigs writing jokes for others.