It might be easier and cheaper to just find a complete (used) display unit on craigslist or eBay (I know well that can be a cr*apshoot, but there ain't too many alternatives).
Snag one and then cannabilize it, or your own unit, as to condition. This is almost always cheaper and more expedient than buying
new (or refurb) replacement parts
from Ray (or other mfgs), dealers, etc. This strategy applies to stuff like you have, for new stuff, reliable engine
parts, etc., it may be best to get the OEM stuff (which can also sometimes be found this way too).
Most of my instrument suite is older gen RAymarine/JRC too, have replaced a few components this way.
eBay has an automated 'search' function in which you specify what you are looking for (and getting/wording the search terms can be tricky for some things, an * can be your friend, or not; you can also deselect terms), then eBay emails you a daily message (if a item is found) with a link to the new auction
item listing (the search function runs for about six months unless you terminate it).
Then you do the usual bidding if desired on a particular item.
I have a number of these auto searches in their system, and every morning I get notified of new listings available on parts/stuff I am looking for.
It's painless, set it up and just have a look at the emails as they come in (or not).
That generation of Raymarine turns up frequently, so you shouldn't have much trouble finding some (new to you) head
units worth bidding on.
Of course you can just login and run an instant search too, I've missed a few great deals by waiting on the daily notification to come across, while somebody else snapped the items up by searching proactively (the eBay auto search is a batch operation, they just process it once a day AFAIK).