Jewlz, egg white powder can be found at Tesco or Sainsburys. Never had a problem finding it on the shelves in my area.
My husband buys Crisco for me in London or we get it online. I have been tempted to try Trex and I do use it some baking, but I am quite concerned about consistency. Crisco is really smooth, where Trex doesn't appear quite so processed. That leads me to concerns over whether it will full incorporate into the sugar and if you don't, it will split later on.
Would be interested to hear whether it works for anyone!