It looks like the barrel band screw itself is ok, so I think Homer is on the right track that he must be looking to replace the "band keeper" screw. It looks like there is a pretty large hole there so you might have to get some wood dough or some other type of wood filler product and fill in the hole. I would suggest mixing a drop or two of dark stain into the wood dough before filling the hole. Then head down to the hardware store and find a very small round-head wood screw. If you have some gun blue you can darken the screw too. The cool thing about having the keeper screws is that the rifles usually shoot better with the band screws loosened, so the keeper screw holds everything in place.