If you are associated with a 501(c)(3) not-for-profit organization, you should check into IRS Form 990-N. Your organization may be required to file this document or face loss 0f status.
The IRS site is: http://www.irs.gov/charities/article/0,,id=169250,00.html.
By clicking on "here" in the box titled "How to File", you will be taken to a place where you can try to register as a new user. You'll need to enter the organization's 9-digit EIN - when you enter the EIN the system will kick you out if you are not required to file Form 990-N.
If you don't know if your organization is still registered as a not-for-profit you can check by going to the Missouri Secretary of State site: https://www.sos.mo.gov/BusinessEntity/soskb/csearch.asp
and searching for your organization.