The 5 hp chipper I got from Lowes twenty years ago came with a bag. I got a larger bag from there later, so I know at least back then they were available.
Wm
My portable self powered chipper came with a mesh bag. Once I threw it in the hopper to store it. Next time I used it months later...yep- forgot about it and started it up and sucked the bag in, jammed it right up
Anyway I found a large mesh laundry bag to use as a replacment.
You can make some bags. I would guess the material will need to be tough suck as burlap, or canvas. I some coco bean bags that would probably work great.
Or, it could be a catcher made of rigid material, like a trash can, or something similar.
I have a Bearcat without a blower that dumps the chips out the bottom. I throw a tarp under before I set it down when I want to collect the chips. Any kind of bag would fill up fairly quickly. As it is chips build up under the chipper regularly so I just raise the 3pt, pull the tarp over a bit and set it back down. When I figure I can still lift it I grab the four corners of the tarp and dump it in a trailer. I tied the box and bag approach and it just seemed to be a PITA -- JMHO