As far as I know, apart from some track available under the LifeLike
brand, all modern track is nickel silver. You can mix and match any
brands of track as long as:
a) the rail is the same code (measured in 1/100ths of an inch, ie code
100 rail is 0.100" high);
and
b) it's plain track with no plastic ballast base.
You may have some issues with curves, since there is no standard for
"1st radius" etc; these vary from one manufacturer to another. Most
trainsets come with 18" radius curves, the rest (aimed especially at
younger modellers) come with 15" radius curves.
Google is your friend:
http://www.hornby.com/
and:
http://www.hornby.com/shop/track/
This site also has useful information (quite a bit, so allow some time
for reading it all):
http://www.newrailwaymodellers.co.uk/track%20layout.htm
The main problem with Hornby is that their wheel profiles have changed,
so that old stock with old wheels will not run run well on modern track,
especially through the points. The cure is to change the wheels.
Caveat: Older Hornby trains are collectors items, so if you want to
maintain their value, you should not modify them (such as changing wheels).
--
Best,
Wolf K
kirkwood40.blogspot.ca