Geoptik makes them:
http://www.teleskop-express.de/shop/...ototripod.html
http://www.teleskop-express.de/shop/...4--thread.html
Here's another one for M48 (you could use a step down ring to M42):
http://www.teleskop-express.de/shop/...m-length-.html
Several CCD manufacturers make them tailored for their own cameras, e.g. SBIG for their ST-8300 (I have one of these):
http://www.sbig.com/Canon-EOS-Lens-A...r-ST-8300.html
Peter Tan in Hong Kong used to stock some very cheap adapters; not sure if he still does.
The main thing is to make sure that you can get the correct ~ 44 mm (EOS) spacing between the lens and the CCD chip. First step would be to find out what the minimum back focus requirements of your 237A is.
Hope this helps!