Non-MAX kolar barrels and non-750 bore barrels just aren't selling.
I know where there's a top single for $1500 that has zero interest, and another at $1800 thats the same situation.
The biggest problem is that the vast majority of Kolar trap guns are/were sold as combos. So the people wanting a single barrel already have one. So your market is someone who has a kolar trap with just o/u barrels (unlikely) or a skeet or sporting shooter (who usually aren't willing to drop a couple grand into a barrel they will only occasionally use).
I'm the latter. I have a kolar o/u skeet gun, and have thought about buying a top single or unsingle for it for trap, but can't justify it for the half dozen rounds of trap I shoot every year. The 1187 I just bought will work perfectly find for that, as will the o/u barrels of my Kolar (which i've been using for years now).