I found this in my latest Ancestry newsletter: If you had a relative whom you know immigrated to the US and you know his/her year of birth you can ask the USCIS to search their records for your relative's records.
The website is: http://www.uscis.gov/portal/site/uscis
Click on Services and Benefits in the upper left end of the tool bar under the official logo, then on Genealogy. Read the Frequently Asked Questions!!! You don't even need to know an exact spelling of the name.
If the birth date of your relative is less than 100 years before the date of your request, then you must provide proof of death but there are many options of acceptable docuements.
This is a pay for services site. $20 for an index search to get the file number. Another $20-35 for the records depending on what type of record it is.
There is a ton of information here. Take a look!
Carol