I don't understand why locating hydraulic seals is an issue. Most seals are used in multiple applications, just like bearings, bolts, nuts, etc. Because of that, seal manufacturers standardize the sizes to minimize their inventories. If you have the old seals and a magnifying glass, there are numbers on the seal which identify it by manufacturer, size, and material. Most hydraulic shops can help you.
That said, some seals are not designed to be serviced because of how they are installed. If your jacks are like that, you may be buying new ones.
Chum lee