rusty body mount bracket

Took my car for an MOT the other day and it passed with a few advisories.
One of which was the front o/s body mount is rusty.
I had a chat with him and he said very probably next year it will need welding. It doesn't seem to have any holes yet but it does feel on the cusp of rotting.
Is it a matter of fabricating some plates or are they available complete to weld on to the chassis? A bit like landrover outriggers etc??

Which mount, front as in under headlamp or just behind A pillar? You can also split these into body or chassis.
Only question as most MOT testers can't actually see the front (headlamp) mount, it's hidden by the wheel arch liner.
Not aware you can get panels with the exception of the front slam panel which has the front body mount, it's the bit that usually rots.

Under the sill just behind the front arch. I just wondered if anyone made aftermarket ones rather than patch it up or fabricate something.

Ah ok. a few on here have repaired that section. 
From memory all had made sections themselves, this backs up my feeling that no off the shelf repair sections are available.
The body mount at this point looks tricky, most have cut out the floor above to access the rot and repair. The chassis a little easier, a new one can be made and welded on "as a Land Rover" out rigger.
A lot will depend how bad the rot is.
A photo would help if you want feedback from those that have done this type of repair.
 

For what its worth, I discovered this too after a fairly aggressive attack with a needle gun, the solid looking mount turned into emmentaler cheese, and this was one of the (5) reasons I lifted the body. Four of the other mounts reacted similarly to my subtle stimulation.

The body repair wizard rebuilt the "arms" and welded a plate on the underside (the top was actually fine go figure). One mod we did to all the plates welded to the underside of the bodymounts was to include meaningful drain holes up against the chassis. The new welds were painted, rustproofed then the insides of the mounts were sprayed with something similar to (but not) waxoyl (?). Not sure what it was..