How to close in space between floor and chimney?

Pardon my ignorance in this wood stove issue but I need a little help.....I live in an old 2 story house. The wood stove is on the main floor with the chimney going up through the floor of the 2nd floor laundry room....on up through that ceiling and to the outside. The space between the floor and chimney has a large gap in it where debris/dust/etc. can fall down. Right now we have a makeshift barrier there but we cannot find the proper fitting for this purpose. Is it called a firestop?? We see the ones where the "collar " goes on the ceiling BUT we cannot see the floor ones...we went to Canadian Tire and Kent but they do not have anything. I wondered if we might make one out of sheet metal and using a rivot gun (just something I might have seen on tv once...).....and would this be approved by an inspector? Any ideas/suggestions on this? We live in a small town and do not have large stores to buy proper attachments for this type of thing.