I cheated slightly as I have been looking to get some age correct bar ends for my latest build recently and was looking at the MOMBAT timeline page only a week or so ago. Ended up finding some NOS onza steel bar ends from 91 that fitted the bill perfectly and they used the exact same end cap.
I'd say they were rarer than Ti's as I've never seen a set on offer, even back in the day the first I saw were the 2nd gen quill steel ones rather than these.
As far as the earliest ones, if we assume MTB ones as similar things have been used on road bikes back into history, I'd say Moots, 84/85? with their lovely wooden ones!