If you need to adapt a lens, names like Wooden Camera, Duclos, Fotodiox, and Metabones come to mind. But if you're in the U.K., MTF Services probably shoots to the top.
The company is known for its lens adapters and has gained popularity after offering Fujifilm MK to Sony FZ and Micro Four Thirds adapters. It now has conversions for Sirui anamorphics in either Canon RF or L-mount, as well as a conversion kit for Fujinon's MK lenses to RF mount.
Sirui offers two anamorphic lenses, a 35mm F1.8 and 50mm F1.8. Both have a 1.33x squeeze and cover APS-C sensors. They're great lenses but are only available in Sony E-mount, Fujifilm X-Mount, and Micro Four Thirds. That generally covers the majority of shooters besides Nikon's DX, but now with the Canon C70, the RED Komodo, and the Panasonic S series having a Super 35 mode, the conversions from MTF Services are a welcome addition.
The converted lenses are based on the Micro Four Thirds versions of the Sirui anamorphics. The lenses will fully cover the image circle of the RED Komodo and the Canon C70, which can create 4K 2.4:1 anamorphic images. Additionally, the lens will cover the sensor of the Canon EOS R when shooting 4K because of the 1.7x crop on the sensor.
Check that out: there is a benefit to having a full-frame cropped sensor.
As for EOS R5 and R6 shooters, because of the full-frame sensor, there will be vignetting on the edges with an approx. 1.35x crop.
For those with a Panasonic LUMIX S1H, S1, and S5 camera, you can switch over to 4K Super 35 or 3.5K 4:3 anamorphic modes to use the Sirui lenses without crop. Both lenses have an image circle that covers the Super 35 mode, and once de-squeezed, the image offers close to a 2.35:1 ratio. In 3.5K 4:3 mode, you will still get a 16:9 image.
Like the RF conversion, when shooting full-frame there's an approximate 1.35x crop with vignetting.
If you already own the Micro Four Thirds version of the Sirui lens, the RF or L-mount conversion costs £150 ($200 USD) plus tax and shipping.
MFT Services also offers a kit to convert the native mount of Fujinon MK lenses to RF. This is a similar service offered by Duclos. The kit comes with a replacement collar, MTF stainless steel RF mount, light baffle, fixing screws, and rear lens cap. Though it can be purchased on MTF Service's website, it should be installed by an authorized engineer.
When installed, the converted Fujinon MK cine lens fully covers the Super 35 sensor in 16x9 on both the RED Komodo and Canon C70. The MK 50-135mm T2.9 also fully covers the wider 17:9 (open gate) mode of the RED Komodo at all focal lengths and T-stops.
Expected coverage of adapted Fujinon MK 18-55mm T2.9 on RED Komodo 6K 17:9
The MK 18-55mm T2.9 covers the Komodo 17:9 mode at wider apertures but will exhibit some corner shading at its widest end from 20mm to 18mm when stopped down. From 21mm up it fully covers the sensor area.
The conversion kit for the MK 18-55mm T2.9 or MK 50-135mm T2.9 costs £325 (+ VAT) ($440 USD). The company also offers a conversion kit for MK lenses for L-mount too, which costs £225 (+ VAT) ($305 USD).
You can find out more on the MFT Services website.