Look at your local Building Department's website or ask them specifically which codes they use so you can get books or other information that matches the enforcement. You also want to know if they are in the process of updating their enforcement and when the change would go into effect. If they change codes the day before your design is submitted, you may have to make design changes to meet the newly adopted code. I've had commercial projects that required design changes because a new code or requirement went into effect between permit application and permit issuance - that's always fun. No point spending the money to comply with 2012 code if 2003 is being enforced unless you want to out of personal preference.
You need to know what local amendments to the codes have been adopted in your town or county. Local authority always has the ability to delete provisions of a code to make it more stringent. By law, they have to make the actual code and any amendments available to anyone that requests it. This may mean a public copy that you have to review in their office or a download on their site.
The IBC and IRC are available to view online for free - can't remember if you can download them or not. You should also be able to find all of the other International Code Series too.
Another good source of information are websites such as
municode.com which acts as a library of all laws for towns that are part of the service. Municode is just one example - there are others if you look for them.
