This link to Mountain Colors
works. The yarn at the top of the list is 4/8, and it is a worsted weight. Does the sweater you're thinking of differ from the one in this link
It's hard to beat the colorways Mountain Colors, one of my earliest projects was Cat Bordhi's "Your First Moebius"
knitted in the 4/8. This was a cowl that saw some good use in it's day, and being that it was worn close to the neck, and myself experiencing "itchiness" from certain wools, I can attest to the wearability of this yarn.
That cowl met it's demise but fortunately was resurrected, like a Phoenix from the ashes