With all the aftermarket "add ons" available for FX, why is it this is not a easier option to get yet?

[elh0102]

I have no idea how the FX factory sets up these guns as far as pellet type and optimum settings. Fortunately, we have good dealers who will set them up the way you want it. That remains a problem for the neophyte who has no idea about this stuff.

I don't think FX "sets them up" at all. They make these adjustamatics under the marketing scheme of a rifle for all seasons. You buy it, then have fun playing with all the combinations.
Back to the original question of after-market barrels. They are available from LW, TJ, etc. But every rifle maker uses a different attachment to the action, so it would not be practical for the barrel makers to attempt to inventory barrels. The machine work required for most of them is straight forward, so like shooters of cartridge rifles, you get the blank to the smith and he does the fitting. A big challenge, most of the techs who claim to have custom work capability, do not. Most of them are competent for general maintenance and tuning work only. I guess it's just the current state of the market. It will evolve.