Adding to what has been posted, four Chinese Maxims, complete with all accessories, were brought to the US at some arund WWII, IIRC, for evaluation and are still in the US. If not all four, at least two of these were registered pre '68 and are in private collections. There are two others that are orignal guns, one of which belonged to Dolf goldsmith in the seventies, of which there was no orignal registration on file in the NFRTR. This gun was finally validated as a C+R a couple years ago with the help of Gary Schaible at ATF.
At least half of the kits that Dolf brought into the US were built into transferables pre '86, with newly manufactured sideplates by Collector's Corner, an earlier incarnation of Ohio Ordnance. IMA had a number of kits several years ago, but I don't recall where they came from. I still have one of the IMA kits with the tripod.
Locks seem to show up now and then for the 24s, but all other parts seem to be very scarce.