I just got a free UCL lens that fits (barely) my P60 hosts! At my office, they were changing the bulb assembly in our NEC digital projector. They had removed the old assembly and I rescued it from the trash can as it looked interesting. The bulb/reflector module had a thick UCL AR-coated lens that is close enough to the right size to fit my 504b with the MF/UF XM-L drop-in.
Not bad for what I paid...
$)
<edit>Who knows? Maybe it's sapphire-glass!