I bumped into some street lighting engineers and was kindly allowed a scrounge around their pickup.

The first item I found was this Holophane 4125 bowl. It had been hit by something, causing extensive cracking over half of the bowl. However, it was rare enough for me to save it.

I haven't checked yet, but I assume the remains of the bowl ring to be from a REVO Prefect. Therefore, if that's true, I'll try to get hold of another Prefect, and fit this prismatic bowl.