I don't know if these count as "retro", but Gun Parts/Numrich appears to have NOS/New Production stripped C7 uppers in stock, at $159.95  here  . I ordered one yesterday, to see what they look like (and for an Israeli carbine build). I'll let folks know and try and post pics once it gets here, if folks want.
Stock photo from their site, dunno if it's representative or not:
http://www.gunpartscorp.com/pub/ProductImage/555810.jpg

I would expect that those are modern Anchor Harvey forgings, machined by LAR, and as used by DPMS and Bushmaster.

The description says made by Bushmaster.

Paladin

Needs a Devtek.

It certainly looks like the one I recently got from DPMS.

The C7 showed up today, and is going back tomorrow: the charging handle cut at the rear is out of spec, about 1.5mm too low, the receiver won't close if the charging handle is forward, and if you close it with the charging handle pulled back, the charging handle binds up when moved forward. Tried it on four different lowers with three different charging handles.
For what it's worth it's brand new, no forge-marks that I can find on it anywhere, black anodized. We'll see what customer support  has to say. I intend to ask for a replacement, hopefully that one will be in-spec.

Sadly, during the recent craziness, some manufacturers were turning out whatever crap they could just to get product out the door. With AR parts and rifles quality control, it's going to be caveat emptor now more than ever.

Wonder if this is the same upper.
Charging handle has the same "N" mark.
M-4 feed ramps..
This came off a newish Freedom Group Bushmaster I acquired the upper off of.