You could try posting ad's at local vet clinics,pet stores, your school,etc... sometimes you may find someone who wants to adopt. As a neighbor you know well or family member too if you know they like cats.
But dont give a kitten away for free, a potential owner should pay something for a kitten.
There are some bad people who will adopt cats/kittens and send them away to laboratories, there called "bunchers"
So you must always be careful when giving away a pet.
Be Careful my Brother put Kittens on Craigsist last Nov and got strange replies. I took the Black and White Girl Kitten and my Sisters Bf took the Tiger Striped boy. It was a 2 hour Drive but worth it. I had told them when they were born I would take either the black one or black and white one. His friend took the black one.
You should talk to the humane society about getting her spayed! They can get you a real bargain on the surgery, or refer you to somebody who can. I'm just saying, because you probably can't afford spay after all the kitten expenses...
So she's 4 weeks pregnant?? I would think you would probably have to find people you know, because no one can tell by looking at the mom what the kittens are going to look like! So unless you want to wait till they are born to show them around and get potential rehomers! After they are born you will have 12-14 weeks with them to post pictures and stuff, IF you go through with the pregnancy. There is always that option you know.... Depending on where you live and how overpopulated your cats are there! In my area there isn't a problem with overpopulation really, but in some areas of the world there is a huge overpopulation problem and rehoming them can become difficult!!
So my advice would be to wait till they are born and post pics! That way people can see what they look like!