In reply to lee birtwistle:
As long as you get a pair of 'suspension corrected' ridged forks you will be good to go.
A few companies make them, those On-one forks listed above are probably a good bet.
Make sure you check wheel size (i.e probably 26 inch wheels on your mtb, newer 29 and 27.5 wheels often used on mtb).
Check the fork steerer tube diameter. It will probably be 1.1/8th inch, but newer mtbs (last 8 years or so) can have tapered steerer tube, which are larger (1.5 inch) at the bottom than at the top.
I have a pair of Kona Project Two forks that I used for the same purpose. about £50 quid at the time, not sure if they still sell them new but can pick them up on ebay I would think.