I've bought & Sold a fair number of .50BMG Uppers, but haven't bought any since ATF spanked Walter at Safety Harbor. (I think his were the best!)
Just wondering who if anybody is still offering them or if I have to search out a complete Rifle?

Try Safety Harbor!

Safety harbor seems perpetually out of stock.

But looking at the various companies and having owned a few they are far and away the best.

Just buy an AR50.  You will be happy you did.  I bought a complete rifle from Walter, can't remember the model number...RN50 I think.  Had chamber issues and stuck cases after firing.  Sent it back and a month later it still had chamber issues...only half as many.  Got fed up a d returned it and got an AR50.  Not an issue with the AR50.  Yeah....it's heavy...but it works every time.

From what I've viewed on YouTube, McCutchen, FKA Zel Custom, is to be avoided.  There are plenty of cheap BOHICA's out there if money is an issue.  Serbu BFG50 might be an option.  Not pretty but no one complains about them....except the wait time.

This is the way.

I have used the Armalite AR-50 and it's outstanding...
One of the Wholesalers we've used has run Armalites on special for $3,500. But for no more than I do/did shoot one, that's about $2K more than I wanted to plunk down.

Guy I worked with has a Brother that developed specialized ammo for Uncle Sam, so they bought a Barrett M107 and there was talk of selling it as they weren't really using it anymore.

We had a Bushmaster .50 come into the Shop and I should have, even could have bought it, but didn't.

I have bought multiple Safety Harbor .50's and the only problem I ever encountered was the knucklehead we sold one to managed to break the Bolt handle off, so Walter sent him a new on at no charge...was buying them during our Bi-Annual visit to Knob Creek, but ATF pulled the plug on his Uppers.

Had a "Custom" single-shot of unknown manufacture...heavy was an understatement, 36" Barrel and Bench Rest Stock...shot good, but it must have gone 35 pounds.

Bought two of the BOHICS when they first came out...had problems with light hammer strikes; cleaned up, polished and with a heavier spring (and maybe hammer, don't remember) they shot just fine.

Guess it's because I've got enough stuff and equipment to reload hundreds of rounds of .50 that's pushing me to find another one.

I have quite a bit of components as well.  I bought cheap and stacked....except for primers...they were never cheap.  I cherish the last 400 I have that I got at $180/500.  They are twice that much now.   I'm still reloading M-8 for .90 and M-33 for $1.10 with virgin WC867.