Here is Slavich's USA distributor for holography supplies.
http://www.geola.com/holomaterials_usa_eshop.htm
and here's another distributor--
http://www.laserreflections.com/film.html
Would the 4x5" panchromatic plates be the same as 102mm x 127mm PFG-03C Plates for $220? They also come in blue-green sensitive, which may be just an ordinary orthochromatic emulsion.
Still costly, but if the materials are the same, maybe it's better just to order them from someplace that is already selling them in quantity, or alternately, maybe this is another market that J&C might consider expanding into--holography supplies.
I know plates were used in Russia for serious photography until surprisingly recently (like the 1950s or maybe even later), but it's hard to believe that they could survive making plates for pictorial photography in the post-Soviet era.