Old IRS forms can be found on the Prior Year Products Page. Most people are looking for “Form 1040” for a personal tax return, so just type “1040” in the search box and you will see all the older years popup. If it is a different form, just use the form number to find it.
Getting old tax return forms might be difficult depending on the wording you use. They are actually listed under Prior Year Forms here http://www.irs.gov/Forms-&-Pubs/Prior-Year-Forms. You can search 1040 for your basic individual income tax return, 1120 for corporate income tax, 941 for payroll tax, 940 for unemployment tax.
Video on getting old IRS forms:
Old FTB forms can be found on their 2010 and Prior Year Tax Forms Page for items older than 2010. Franchise Tax Board is the state income tax entity for California. The standard income tax form for California is “Form 540.” 2011, 2012, 2013, 2014 and 2015 forms can be found on the regular FTB Forms and Publications Page.
Video on getting old FTB forms:
This list will be updated with other old tax forms from time to time.