So you mean the FC mod? Meaning you want alternative 29 mm downstem percs, for 18.8 mm female connection? I think the one that comes with is the best personally, but you can try to get the old FC mod percs from them or another seller (the matrix and the circ) some people call that modular toro rig and ash catch from other sellers, and I think the tree perc from the sunshine store sheldon black is the same size to fit as well? None of these are sold separately, you would have to message the stores and ask if they can sell you the individual pieces... Or you can search for 29 mm down stems on eBay or another online store somewhere, even a head shop should have some really?
Like I said mouthpieces are trickier, there are not a lot of 18 male mouthpieces, but Genesis makes a couple now with spikes for us, the one that comes with the new FC mod is actually very solid, you can get other custom ones made from US workers, an angle adapter can turn any basic 18 male mouthpiece usable with 45° angle... There are a lot of options but not necessarily from China, GVB and pyro tech Phineas and Rogue can all do them too and have