That is the site. To get the adapter you will have to call 3sx. They do not carry them on the website except in their kits. Or you can just check on ebay. Make sure you get the 7" cone filter with a 4.5" connecting end.
As for the Throttle Plate
I'm assuming he is talking about the small plate on the throttle cable. It is just behind the intake plenium. A small steel braided wire runs through it. You might check it out and see if there is anything wrong, although I don't know exactly what to tell you to look for.
The throttle body bore from Dynamic Racing is apparently cheaper than the one from GT PRO (Not suprisingly) since the cam regrind from DR is $750 and you get 100 hp Nitrous Jets with the stage upgrade all for $1000. So I'd assume just the bore would be $200 to $150.