I got it from the states, no one locally that deals Fister products afaik, though you could get a local exhaust shop to have a go at replicating the Fister mod if you’re game..
I did the core return option, it’s the only option unless you want to pay for them to modify a brand new set and send those to you (1300USD PLUS the cost of modification and shipping - no thanks!).
I had absolutely no issues with shipping either direction. They arrived within a week of posting on the way here, and I sent mine back to them last Thursday via Pack and Send (onto DHL) for ~$350 (cheapest I could find) and they arrived today.
Not the cheapest option, but a good product and easy experience.
DM if you need any help 👍🏼