Hi Jason, welcome to the Mud Club. :D
Another good place for some parts is eBay, you'll be suprised what you'll find on there for a Disco!!
Before you start getting things like mud tyres etc, have a good think about what you want the vehicle to do in the end.
If your thinking about larger tyres then you're going to need a suspension lift as RRB suggested, this can create a whole new set of problems to the steering and propshafts etc. It may also require a trimming of the wheel arches so the tyres don't rub on full articualtion.
It can be as expensive or as cheap as you want to make it. Look at all the options and have a good search through this forum to see the good and the bad. When you know what you want to do you can then budget for it and learn for everyone elses mistakes!
It's taken me over 5 years and several bad calls to get my Disco to what it is now so there is no rush because, as RRB has said, you already have a capable 4x4 there. :D
When I got my Disco it looked like this:
.......and now it looks like this:
If you have a look at my profile there is a list of everything that I've added over the years. :D
