Found this in all places a web site selling lawn mower equipment. They deal in over stock mower parts and the like.
A Delta canister filter part number 50-750. Fits Delta 50-850 dust collector. Amazon lists it for $243.09. This place has it for $109.95. I know nothing about this filter but thought I would pass it along so someone needing such item could check it out.
http://www.smallenginewarehouse.com/...amp+and+gasket