There are a number of Certificate Authorities where this information can be purchased. Be sure your certificate requires a password or pin number. If it doesn't, then anyone using your computer could sign a document. You may want to have more than one certificate so that your agreement with customer A uses a different encryption than the one for customer B. Selecting a proper password is also crucial to maintaining proper security. First you do not want to select words for your password.
Programs are available that attempt to decipher passwords.
The easiest to decode are those using words. The best passwords contain a combination of upper and lower case letters, numbers, symbols and include at least eight characters. Your passwords should not be written down. The best ideas I have seen for creating passwords involve following a consistent naming method that would only make sense to the creator. In the future, I expect our computers will use an eye or finger print scanner to code and create your private key.