I looked for several months and never found a decent used set. After several swapmeets, daily Craigslist searches and a WTB post, I ended up buying a new set off Ebay. These imported manifolds weren't my first choice, but I finally bit the bullet and bought them. Nice to know they're new - no cracks, flat mating surfaces, nice clean castings. I specifically searched for a new set with no tapped smog fitting holes, since my K20 never had a smog pump. The set in the link below is what I purchased. They have the smog tube bosses, just not drilled and tapped. These were the cleanest I could find at the time at a cheap price.
I finally bought this set for $95 (negotiated with the seller via make offer option on Ebay) with free shipping. The quality looks good. Also, both manifolds have the chamfer machined in so you can run an exhaust doughnut on both sides and eliminate the exhaust heat riser/spacer, if desired.
https://www.ebay.com/itm/L-R-Pair-Ch...72.m2749.l2649