Honestly, a call to Heliproz, Helihobby, or Zooms will have shiny new Shuttle parts on your door step before you could find them at the local hobby shop.
I've replaced the gyro with a JR 410 tail lock and the tail servo with a JR810G which is a fantastic combo. Got the gyro off ebay for about $75 or so, the servo is new for $64 bucks.
I also upgraded to a set of Funkey fiberglass blades that worked awesome. Century makes a killer set of mufflers that keep the noise down and performance up!
I have seen new start belts sold here and there but the O.S. .32 pull start that I have in my ZX is a work of art and requires just a glow starter and a few tugs on the rope to get the party started!!! I think its the O.S. 32SX-HX. I'd buy one again in an instant. Its almost not cost effective to upgrade to the top start feature as you can almost by the whole Shuttle Plus for the same cost.
Whatever you do........dont try to make the ZX into a TREX or RAPTOR unless you want some major headaches, besides you already have a belt driven tail on the ZX. If its "Bling" you seek, there are some awesome upgrade metal parts from Quick UK and they ship parts so fast it'll make your head spin.
The ZX is a very capable machine as I'm quickly finding out!
As I've stated in the past..........you cant make a washing machine into a clothes dryer.............unless, of course, you have alot of money.........and even more patience!
Tony