My Soma Double Cross frame comes with downtube shifter pods sticking out of the frame. However there are no housing stops there, so I can't figure out how to run shifting cables on the frame.
Is there some addon I have to buy to convert the downtube shifter thingies into housing guides/stops? I haven't found anything online yet.
2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
Those are similar to what you need although you can get Shimano stops that are nicer and cheaper (they have aluminum bodies). I forget where I found them but it really doesn't matter for you for the following reason. All Shimano, and presumably Campagnolo, STI kits come with shifter stops that bolt on to the frame. The mount for the STI stop is the same as the mount for a downtube shifter allowing you either option. The stops attach with a short socket head screw. Some frames, like my Specialized, do have STI stops built in but I prefer having the just the mounting points as it allows more options.
Almost any shop that handles Shimano or Campy will have that part. Although I ride nothing but Campy parts I use the Shimano cable stops because they look better than the campy equivalent. Both work...
Unless you bought the bike assembled normally the bikes don't come with the cable stops unless the bike has braze on fittings. You usually still need the screw in adjustors.
I used the same Shimano adjusters and had my BB shell chased, but didn't really seem to need it. Also, external bearing BBs don't seem to spin as freely as cartridge under no-load, so I wouldn't worry much about that, either.