There used to be some good sites I used. Problem is, most older D3 players finished those achievements ages ago, and I don’t know if anyone updated the old lists after additional enemies were added to the rift pool.
Although I guess the good news is that if you can find an old site that lists enemies that do/don’t spawn in rifts, I don’t think any enemies were removed from the rift pool, only added. So some of the enemies on the list that didn’t used to spawn in rifts might now, but you know any enemies that were listed as spawning in rifts before definitely still should now.
There’s definitely still lists kicking of non-rift zones where each enemy spawns, and those should still be accurate. Although I remember there being one pretty popular list that was for sure inaccurate, I think it’s this one: We Are the Champions - Diablo Wiki It’s been a while, but IIRC it lists enemies in zones where blues/yellows of that type cannot spawn. I think the best example I’m thinking of is Fallen Cur, I don’t think Champion Fallen Curs can spawn in Dalghur Oasis or Ancient Path, only in the fallen-type mob spawn in Storm Halls (there’s two types of mob spawns in Storm Halls, you’ll only get the Fallen Cur champion pack if fallen-type enemies spawn here). I seem to remember there were a few more like this on that list too. Don’t use that one (or the Trophy Hunting list on that same site)
EDIT: I remember there being a really good site I used to use, but I can’t seem to find it anymore. It might have been taken down.
EDIT2: This might be helpful for enemies that spawn in rifts: http://www.warpath.eu/mp.html
This looks like a good list for We Are the Champions and Trophy Hunting: Elite Monster Achievement Hunting Guide — DiabloHub
And this looks good for No Time For Losers: Achievement Guide: Stamp the Champs / No Time for Losers | Nephalem Notes
And the Trophy Life: Achievement Guide: A Rare Breed / The Trophy Life | Nephalem Notes
EDIT3: Oh also for the yellows, always wear/cube Nemesis bracers and click any shrines in the zones where the yellows you are hunting can spawn. There’s a chance the shrine will spawn the yellow pack you need.
If you’re on NA servers, join the Achievement Hunters community. It’s not as active as it used to be as many members finished their lists a long time ago, but a bunch of us still hang out there and might be able to remember some tricks or offer some advice on ones you are missing.