Do you live within walking/running distance of a park with a playground? If so go there and you can do pullups on the monkey bars. If not find a tree with a low branch and do them there. You can pretty much do pullups anywhere you can get your knees off the ground. This video will give you an idea about the many places you can do pullups.
His site has some great information on it so give it a read.
- Mark S PIE'd this