In order to get government contracts, you must learn how to be a part of the system. Each government entity has its own procedure which can make the process tedious and difficult. Start off by making contact with the purchasing agent of the agency or department in which you are interested. You will generally receive forms to get on their vendor list. Being on the vendor list does not, however, guarantee any contracts.
Back issues are also online.
State and local contracts are advertised in other venues. Contact your state and local agencies to learn how to keep up with contracts of interest. Some state contract registers are on the Internet. When a suitable contract is advertised, you need to respond correctly. Sometimes a formal proposal is required, sometimes an informal bid will suffice.