I wanted to up grade to a posi rear end, i have a 10 bolt right now can i up grade to a 12 bolt posi? and where would be a good place to get one?

You can put a 12 bolt in no problem. You will need, however, either a new driveshaft to fit or have your's shortened and fitted with the correct U joint. Best place to get one would most likely be a swap meet although you will pay out the wazoo for one. They are going anywhere from $600-$1500 depending on gear ratio and condition.