This article is from the Paper Money Collecting FAQ, by Bruce Giese firstname.lastname@example.org with numerous contributions by others.
The Bureau of Engraving and Printing (BEP) sells various sheets
of uncut 1 and 2 dollar notes (4, 16, and 32 per sheet) through
the mail. They cycle through the various Federal Reserve Banks
over time. The cost varies from $10.25 (4 one dollar notes) to
$79.00 (32 two dollar notes in a cardboard frame). You can order
Order Processing Center
Bureau of Engraving and Printing
P.O. Box 371594
Pittsburgh, PA 15250-7594
They take checks, Visa, MC, or money order.
Sheets may be ordered flat or rolled, and,
officially, take 4-6 weeks to ship but may vary
a lot more than that.