I went back late last night and re-Googled Thompson Center Hawken Pro 550 and got a hit.
The hit was on Ebay and was for a trigger guard fitting this mysterious model. Clicked on the Ebay link and couldn't find the trigger guard.
Trigger guards for everything else. Just not the one advertised.
Maybe it wouldn't show due to what bigminnow
said "auction is closed".
And tonight, I can't even re-find the hit when I Google it.
But it did say Thompson Center Hawken Pro 550.