In the ‘50s, my mom was piecing a quilt top on her old Singer treadle machine, and she was very pregnant with my brother. So I sat on one side of the machine and worked the treadle while she sat on the normal side doing the actual sewing. (The weird things you remember!!)
Apparently, new machines that don’t requir electricity are still being made — probably for the Amish, etc. Probably not a bad investment just to have on hand for SHTF.
I'll bet you could find them in this catalog.
Lehman's Non-Electric Catalog