Yes I'm aware of gobig having brass but its sold out. Also, I understand necking down is easy, but with a bushing die it will most likely leave a donut I don't feel like dealing with.
Seems I can use 22-250 brass from what I've read.
I doubt you will have a donut. I started running a 22-284. Ran 6.5x284 brass through the Redding 6x284 FL die, trimmed to spec, then went from that right to a 0.252 bushing, no donut for me. Brass grew 0.004" from after going from 6mm to 22 cal. I think its a safe bet you would see the same result with 6 Creed brass.
If you don't want to neck brass down, id give the 22-250 AI a serious look. Same performance, if not better than the 22 Creed and less picky to load for. My 22-250 AI 8 twist shot everything good from 55gr SGK to a 90gr SMK. 55's at 3900 with RL17 and 90gr SMK's at 3150fps, shot 0.25 MOA at 200m with H1000. My buddy built a 22 Creed and after he saw how my AI shot and how easy it was to load for, he ripped the Creed barrel off and had a AI barrel spun up. Bought a 50 pack of cheap winchester ammo, shot em off, ran em through the sizer, trimmed a bit and he hasn't looked back.
As far as seating stems, I use a 6.5x284 Redding Competition seater for my 22-284 with no issues, I run 75gr Berger VLD, doesnt leave a mark on the lead with 0.004" neck tension. My 20x47 Lapua I use a 6x47 Whidden die, no issues either, 0.003" neck tension.I was nervous about the setup until I tried it. Whidden can make you a custom seating stem, but shipping to Canada is $45 USD for a $9 part. Not worth it when the 6.5 and 6mm stems work fine for the 22 and 20 cal leads.