Commercial-quality film polarizers are available. These linear polarizers have 25% transmittance for unpolarized light.
Holmarc’s Multiple-Order Wave Plates are made from laser grade quartz crystal. These are designed to give retardance of several full waves, plus the required fraction.
Zero order wave plates are made by combining two multiple - order wave plates with their optical axis aligned perpendicular to each other.
Holmarc’s Cemented True Zero-Order wave plates are made of BK7 or equivalent substrate and a true zero-order wave plate.
Fresnel Rhomb retarders give half-wave or quarter-wave retardation nearly independent of wavelengths.
Soleil - Babinet Compensators are zero order wave plates with variable retardation over a wide range of wavelengths.