Hi One of the easiest ways is to use adwords as if you where going to create some adds for that key word, although this will tell you the number of estimated clicks.
You can also use
http://www.miva.com/uk/content/advertiser/landing1.asp the keyword generator wich tells you the number of searches.
And
http://inventory.overture.com/d/sear...ry/suggestion/
Will also tell you the count for search.
Hope this helps