Historical estimates of the density parameter
I found an article by Wendy L. Freedman Determination of cosmological parameters which contained the following graphics

The corresponding references should be listed in the references of that paper
References

The online article is also published as Invited Review given at the Nobel Symposium, Particle Physics and the Universe, Haga Slott, Sweden, August, 1998. Published in Physica Scripta, Vol. T85, 37-46, 2000.
http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/denpar.html offers a value of 1.02 +/- 0.02 and dates back to the 2000s