7" Circular drain covers

[mikeymikec]

Here's what the item that needs replacing looks like:

I've never looked into buying anything vaguely similar before and I'm wondering what to look for. The one that ought to be replaced has a slightly broken grille and looks like cast iron. The drain cover isn't completely/directly exposed to the elements, I bought one of these last year and cut it to fit around the pipes (amateurishly, but a reasonable job IMO) directly over the drain, though it's not completely stopping what appears to be moss from the roof getting in there (every few months I have to scoop the foul-smelling matter out of there):

The environmental conditions go from about -10C to 30C (being the extremes I think).

 

[Greenman]

Try a plumbing supply, not a big box store but an actual supply house.
That looks like a very old school area drain grill.