WTB a high quality bolt carrier. Do NOT need bolt just bolt carrier. What should I buy and where do I buy it?
WTSHTF lightweight build. Gotta work EVERYTIME !

AR15.com store appears to have their carriers with key on sale for 35 still.

This one from AIM comes with the bolt but its only $140. Kinda hard to find a lightweight BCG that isnt totally stripped.

https://www.aimsurplus.com/product.aspx?item=XAIMBCGTICNLW&name=Light+Weight+AIM+AR+.223%2f5.56+Titanium+Carbo-Nitride+9310+MPI+Bolt+Carrier+Group&groupid=12184

Young has stripped lightweight in chrome.

https://youngmanufacturing.net/product-category/bolt-carriers-556/

Sionics sells carriers that are NP3 coated and I've heard they are made by the same company that makes BCM's, which are known as some of the best. That's the route I would go for carrier-only.

ETA: Young mfg is great too

Shipping is expensive. Should offer a USPS option.

I think some items do. It may be based on weight instead of what will fit in a flat rate USPS box. You could probably get 3 or 4 carriers in a small flat rate box but no option for it.

I run the AIM lw nitride BCG in a .300bo pistol, no issues.

The JP is a nice top tier option if this is in your budget.

But it's also just a carrier, as long as the gas key is staked properly IMHO it's good. If this is a 'life or death cannot fail, must run til the earth stops rotating', don't go lightweight, get a good semi auto.

A top tier bolt carrier worth every dollar is the JP Enterprises carrier, full mass:

https://www.opticsplanet.com/jp-enterprises-stainless-full-mass-tactical-carrier.html

Same in low mass:

https://www.opticsplanet.com/jp-enterprises-stainless-lmos-carrier-with-qpq.html

Where to buy is depending on what you're looking for, price point or post-sale service.  I've had great experiences with Brownells, Optics Planet, RTB, and Aim Surplus.  I'm sure there are others around but these are the folks I deal with.
However, more standard units that I've had good experiences with:

https://www.righttobear.com/Mil-Spec-Phosphate-Carrier-w-Gas-Key-p/phclc.htm

https://www.righttobear.com/Anderson-Manufacturing-5-56-223-Bolt-Carrier-car-p/b2-k632-a00.htm

I used JP carriers in all my match rifles, from 223 to 308.  They are the foundations to the match grade BCG in my rifles.  Over 20 years and probably over 20k of 223 through the (3) 223 match rifles, and somewhere north of 4k through my (2) 308 match rifles, zero failures of any sort.

With that said, I've not encountered any issues with standard grade carriers from Colt to Aim Surplus, Right To Bear, and Toolcraft.  As long as the staking is done correctly, they just work since there's much to the carrier.  Chrome lining or QPQ of the inside is important.

I would go with Right To Bear.  I have heard good things about their lightweight carrier and it is priced right