Titleist does not sell any parts for any gear or clubs. I have not checked to see if an old fairway cover has the identical size insert? if it does, you can get old, used covers pretty cheap on ebay. You could also do a DIY fix with a butter dish lid cut to size and a sharpie. Sorry for your loss.

I had a 818H hybrid headcover that used the same insert as the one in my TS headcover. There should be plenty of used Titleist headcovers online to source one from or hopefully someone on here has a spare.