Mike, for what it's worth, no one here has reported on having a fluted .204, the .223 and .22-250 are available, though and a couple here have them, although they don't seem to post a lot on them. My guess is that Green Mountain, the supplier of most of the barrels for Marlin/H&R/NEF, is in short supply of the fluted .204 blanks since the .224 fluted calibers are available.
Tim