door mechanism hole adapter plate thing :-)

I've got a door with a hole of around 2-1/8" in diameter for the handle/ latch mechanism, but the handle/latch assembly I have seems designed for a smaller hole, as the tabs which extend inwards from the back side of the handles (intended to keep the handles centered vertically) are only around 1-3/4" apart.

The plates onto which the handles mount are more than wide enough to cover the 2-1/8" hole; it's just the tabs that stick out from them that aren't far enough apart for what I need.

A picture's worth a thousand words, so mega-quick diagram time:

formatting link

I'm sure I've bought handle/latch kits before that came with a little adapter plate to fit doors such as I have with the larger hole, but this particular one didn't (even though it was branded as a universal kit, rather than "only fits doors with holes of blah blah blah...").

Questions:

1) Do these "adapter plates" have a proper name so I can google?

2) Can they be bought anywhere? (I didn't see them in HD the other day, but haven't checked anywhere else yet as I'm not sure what to ask for)

If it comes to it, I can always make what I need here from a bit of metal plate, but it'd be easier to just buy something if they're not expensive.

cheers

Jules