Right now, the Ascendancy/Engine/Cauldron are not coming together as often as before
It might not be what you're looking for in terms of cmc, but I really like Crystalline Crawler as a support piece as well. Instead of just getting big due to the untapping it helps the engine generate tons of mana.
I might be putting too much stake into the next suggestion, as situational tutors are really hard for me to evaluate from list to list, but:
Has been a favorite of mine. There are a lot of constructs that intersect with supported combos in my list personally:
- XX-robos / Memnite / Phyrexian Walker / Patchwork Automaton / Cathodion for Enduring Renewal
- Scrawling Crawler for wheels
- Myr Battlesphere for Welder
- Triskelion for recursion nonsense
- Just some general cube cards here and there too, like Bomat Courier / Scrapheap Scrounger / Torrential Gearhulk / Metalworker
and of course, Steel Overseer & Crystalline Crawler for Jeskai Ascendency / Intruder Alarm / Paradox Engine.
You have a few Constructs that might be valuable targets:
-Scrap Trawler
-Stridehangar Automaton
Although arguably too clunky outside of niche-tutoring, Recombiner does intersect with counters / sacrifice / welder. I am curiously if it could mesh successfully with your supported strategies while also buffing the consistency of your artifact combo-pieces. (as a slight edit: I personally am a fan of narrow tutors, I like niche strategies being able to reliably draft a tutor most would wheel without a second thought)
As for Green / White counter support , a lot of my personal inclusions angle towards storm / persist / green-aggro / white-humans, and am unsure if any individual suggestion would really assist in your goals. I do run Ozolith, the Shattered Spire and like how it supplements the counter components of strategies I support without being incredibly narrow.