I believe that there is a man in France making reproductions of these.........do a search on E-Bay.......and then look for different reproduction items in an "MG42" search. He also make reproduction "sulpher-containers" for the gunners-kit.
You aren't going to find one in a week or two, it may take a year or two of watching ebay before one is offered for sale.
Other than looks, they suck. Pulling back the bolt with one is very difficult. They were replaced with the new style for a reason - they are difficult to use to operate the gun.
The folks in France making the MG42 repro flat charging handle is "AASsniper98". Great people with a lot of re-produced MG items. Priced in Euros = expensive. Great web catalog.
He is on US Ebay as "miminana83". Do a search for him by seller, then click on any of his products and "ask seller a question" about the MG42 flat charging handle. In the past, he has put an item up on Ebay so that I could "Buy-it-now".
I've heard that, since the flat charging handle offers no "lever-pivot-mechanical advantage" like the later handle...it's a little hard to get the rollers to let loose of the barrel/cam-piece. Harder to cock.
Good luck in your search.....Phil