Do these meet your requirements? ATmega16U4 http://atmel.com/dyn/products/product_card.asp?part_id=4380 http://atmel.com/dyn/products/product_card.asp?part_id=

Do these meet your requirements? ATmega16U4 http://atmel.com/dyn/products/product_card.asp?part_id=4380 http://atmel.com/dyn/products/product_card.asp?part_id=4380 ATmega32U4 http://atmel.com/dyn/products/product_card.asp?part_id=4317 http://atmel.com/dyn/products/product_card.asp?part_id=4317 Or use an AT90USBxxx part like on: http://www.pjrc.com/teensy/index.html http://www.pjrc.com/teensy/index.html