Research by Aaron Starr:
In 1980 Ed Clark received 921,299 votes. He was on the ballot in all 50 states plus DC and the eligible voting population was 159,635,102. He received 0.58% of the vote.
In 1984 David Bergland received 228,705 votes. He was on the ballot in 40 states (including DC). The eligible voting population in those states was 125,361,039 (167,701,904 nationwide). He got 0.18% in those states.
In 1988 Ron Paul received 432,179 votes. He was on the ballot in 47 states (including DC), not getting on the ballot in IN, MO, NC and WV. The eligible voting population in those states was 164,071,681 (173,579,281 nationwide). He got 0.26% in those states.
In 1992 Andre Marrou received 291,627 votes and was on the ballot in all states (including DC). The eligible voting population was 179,655,523. He got 0.16%.
In 1996 Harry Browne received 485,798 votes and was on the ballot in all states (including DC). The eligible voting population was 186,347,044. He got 0.26%.
In 2000 Harry Browne received 384,431 votes and was on the ballot in all states (except for AZ). The eligible voting population in those states was 190,973,735 (194,331,436 nationwide). He got 0.20%.
In 2004 Michael Badnarik received 397,265 votes and was on the ballot everywhere except for NH and OK. The eligible voting population in those states was 199,806,005 (203,483,455 nationwide). He got 0.20%.
In 2008 Bob Barr received 523,713 votes and was on the ballot in all but six states (CT, DC, LA, ME, OK, WV). The eligible voting population in those states was 201,753,869 (213,005,467 nationwide). He got 0.26%.