the ones brownells & midway used to sell were made by meier works and they are no longer in business.
i ocassionaly make a batch of them but right now my lathe is down so i cant make the latch blank or floorplate hole bushing.
i make the lever from 5/16" keystock and a 8-32 screw. i rough shape the lever then drill & tap it for the 8-32 screw. i weld the screw in from the top then file the weld down flush and finish shape the lever. i use a 6-32 set screw on the latch and a 4-40 for the detent. when i do a run its $60 per kit or $100 installed.
here are a few from one of my batches.
one that i installed on a small ring mauser for a guy a while back.
a better pic of the installed lever.