Can I substitute Glucose Syrup for Sugar in cake recipes?
Dextrose in powder form is very easy to get a hold of!  As mentioned before, it is a very common ingredient in brewing, and is readily available from homebrew stores.  While not as cheap as traditional table sugar, it isn't expensive either.  Search online to see if there are any homebrew stores local to you.  

Here's one place to get it.

And another place

And why not one more for good measure