http://www.foia.gov/faq.html#howlong: "In some circumstances the agency will be able to respond to the request within the standard time limit established by the FOIA, which is twenty working days, or approximately one month...When an agency needs an extension of time to respond to your request the component will notify you in writing..."
If you did not receive a letter telling you there would be a delay, your request has been lost somewhere. You could spend time working with the CBP FOIA liaison to locate your request, or you could make an online request that will be completed in a month. I would choose the latter.
