Substitutes for cheesecloth or strainer to make stock?

I have used a double thickness of dry paper towels in a large fine sieve and it has worked perfectly. Be sure to remove visible veggiies
and chicken first.

I have used a clean linen dish towel, works fine and you just need to wash it.

Coffee filter will work, albeit much slower, but nonetheless will work. Set atop a pitcher and carefully ladled into, a coffee filter works fine. Also, try wetting a couple paper towels, then squeezing them dry, placing on top of a colander, setting the colander in a bowl and ladling stock/broth over the paper towels. This is trickier, because the towels may slip, but will yield faster results, than a coffee filter. Also, maybe try letting it settle for a bit, with the heat off, and maybe, just maybe the solids will sink to the bottom, allowing you to skim off/out the broth/stock. Good luck!