Hey Sponge,
Norbar Torque Tools are excellent and I will highly recommend them (it's their main business), but to be fair any torque wrench from a reputable company will be fine... Snap-on, MAC etc.
The only real advice on how to keep a torque wrench is to never store it set at a torque. Set it, use it, then remove the preload. Simples!
You'll probably find though it's not something you will use regularly so it might be better for you to nip down to your local car garage or something with your bike and ask if they will let you use one of theirs if you don't have a mate who has one!