The other possibility, if you live near one of the larger metropolitan areas, is to look for hydraulic repair shops especially those that also sell heavy truck or construction equipment parts. That's a long shot. While the manufacturer seems to have a large presence outside the US, it seems to be far less well known here.
What else uses those transmissions? Foreign made forklifts maybe? If the repair company won't sell parts, try to find out what other equipment uses the transmissions and expand your search to include businesses that repair that equipment.
Depending on the part you need, if it's something like a seal or bearing, you have a lot of other possibilities for sources. Often parts can be machined by a shop and returned to fuctionality. As an example, a shop with the right grinder can usually restore a hydraulic pump that has worn to the point the internal clearances are no longer within spec.