Some folks may pay a premium to get a film that is not available in their local market. For example ILFORD make a Pan100 and Pan 400 that are only sold in a few places. If you REALLY gatta Try it, you have to either visit one of those places or buy from a dealer.
As Far as the Shanghai Seagull GP-3 is is actually not bad film. I have a shanghai Seagul TLR and it is the only film that transports corectly in that camera. The Camera designer counted on the extremely rough texture of the GP3 backing Paper. I do suspect that the Shanghai Film is packed by hand. The rolls are sealed with what looks like Masking tape with a rubber stamped "seal" of a couple of Chineese Charactters.
I still have a few rolls of ERA in 135, but understand that no more will be forthcoming.