Devon 4x4 sells wheel arch flares i'm sure they'd courier them out to you if you couldn't find them else where.
You should be able to get 33" tyres on with the stock suspension and wheel arch flares, you just have to do a bit of cutting to the arches. Also you'll want some wheel spaces or heavily off set rims else you won't have much steering lock.
Personally I'm none too keen on the body lift idea at all, and certainly wouldn't do it to mine.
If you want more axle articulation have a look at
www.scorpion-racing.com they offer two kits. The EXTREME kit is the one to go for as it offers 3" lift and 3" droop capability.
You can run 35" tyres on a Discovery but you run out of room in the front wheel arch which will limited wheel travel, if you can go without that extra bit of clearance then 33" tyres work well.
Here's mine on 33" Simet Jungle Trekker II's with stock suspension:
Here's a discovery on 33" with the EXTREME suspension kit:
I'm pretty sure this one is on 35" tyres, but as you can see it has some major wheel arch flares on it. It also has the EXTREME suspension kit on it:
