Census does not have 2001-2004 PUMS, but iPUMS has 2001-2004 data. Two questions: 1) where are the sources of the 2001-2004 PUMS data in iPUMS? 2) Do the 2001-2004 records have PUMA info?
As @JonathanSchroeder noted in his email directly to you:
(1) The original source for the IPUMS ACS samples (all of them, including 2001-2004) are from the Census Bureau. The PUMS data is available through their FTP site, which is located here. You can also find some basic info on all IPUMS USA samples on this page.
(2) Unfortunately, those samples do not have PUMA info. PUMAs are only available in the ACS from 2005 onward. However, METAREA (and MET2003) is available in the 2003 ACS sample.
Michelle: thanks very much for the explanation.