Someone has posted the internal sales figures for US Atari 7800 from 1986 - 1990, he said he'll post the 2600 data today aswell.
7800 hardware shipments:
1986 286,417
1987 1,313,561
1988 1,423,977
1989 655,353
1990 93,443
Total 3,772,751
This doesn't include 1984 test launch or post 1990 sales, so the total number would be a little higher.
Link