For a modern enlarger, the Saunders/LPL have universal glass carriers available. The smaller formats include masking blades. For the 4500's, the masking blades are a separate assembly that replaces the lower plate where negative carriers sit. Other manufacturers offer the universal carriers, but not too many offer the masking blades.(posted 8402 days ago)You should be able to find a used carrier for this format. Try: http://www.classic-enlargers.com/
You could also try EBay.
For the B22 carriers, though, the negative carriers were quite simple affairs. A good machinist could cut & form these out of aluminum or steel plate. I'd recommend anodizing or applying a good finish to avoid the aluminum from rubbing off onto the negatives.