The external screw on oil filter is a modification for 750 twins, it does not have a sump plug as standard, and the "filter" itself is much larger. I have seen custom made cover available with the external screw. If I recall correct the material thickness on the original cover may be too small and it can not be done to it.
Some brass wire mess of similar size can be bought. Fine brass mesh can be cut with suitable scissor. The thing is kept together with one M6 screw, the mesh is just fold in place, very simple. When put back together, one droplet of locktite to lock the screw back in place. Brass can be generally repaired by soldering, but not recommended in this case as the brass probably has lost some of its Zinc and is therefore brittle and will break down soon again.
