Is there such a thing?  Who makes it?  Does it work OK?

speer (CCI) used to make shot loads for 38,357,and
44mag . Shot was fairly small and as with all shot
run thru a rifled barrel would tend to throw a
donut type of pattern.Some barrel lengths would be
better or worse but results would be generally
spotty-more for pest control than any hunting use.
At one time the empty shot bottles could be had with load spec in the speer pistol reload book.
close work only-snakes and rats at 10-15 ft
NHSPORT

I have not used the "birdshot" in the .44 magnum caliber, but I have used it with the .22 LR in my Ruger New Single Six about a 6" barrel. I would imagine the results are pretty much the same for the .44 mag. At 15 yds. (45 feet) the pattern is scattered, with the small shot spread all over a human size target. It works best around 6 feet (under 1 yard) and out from your feet at least 6 feet. (otherwise you will put the shot into your shoe, boot or foot.) Great for snakes since you don't have a single shot at a moving target. Not good for much else. I have posted a target showing the birdshot at 15 yds. shot at a human sized target. The birdshot is circled in red. at http://www.geocities.com/rugercal480 look under targets and birdshot.
Ruger (Mike)