It actually isn't that hard to make this yourself, and this way you can customize it to your own needs. I did a 4x5 and a 35mm for my LPL 4550. I started with glassless LPL carriers sourced from KHB - which they machined out to oversize. I installed coated optical glass from Schneider. Some careful measuring and shimming to make sure it is precise, but overall not very difficult. The machining by KHB was quite reasonable. High quality optical glass, custom cut is the expensive part.