Young Manufacturing seems to be the only option but they are out of stock, and I don't ever remember seeing them in stock.

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

Looks like 9 in stock to me of SP-1 AR-15.  Out of chrome finish not phosphate.  Probably messed up page location but search carriers on page 2 of addy above for SP-1 replacement.  Also if not in stock  they will make it happen in timely manor more than likely.  Tell them what you, may be best to call.  Haven't bought any in yrs but high quality and still function like new yrs later..  They always did me right.  Perfect choice for replacement or retro clone build.  Little spendy in today's market but one generally gets what they pay for too.  If it's Young it will retain most of it's value over the long haul.

Edit:  My mistake does look like out of stock for M-16 style.  I just looked at SP-1 replacement.   Pics don't show much difference in tail on AR-15 than M-16 style.  Calling them used to work better than e-mail.

Thanks, I will try sending them an email.

I do want the M16 carrier though, so I may be in for a wait.