> I would appreciate any help concerning options for large negatives
> (30x40 or larger) for cyanotype or other processes.
> 
 
Micheal,  Kodak's 4127 can (could) be purchased in rolls.  It did however
require an investment of some $8000.00 US dollars.  It is very similar to
4125 Pro Copy film.  I haven't be involved in a purchase for several
years.  Perhaps there is some out there, It was sold in sheets for
sometime..  Good luck
EJ Neilsen