Here is a website that is good for some screencaps. the screencaps has a lot of images, almost too much. I don't think there is anyway to search by character, but the episode sections seem to be somewhat by scene chronology so if you know the episodes rather well you can probably find some good action screenshots.
http://torchwood.time-and-space.co.uk/v1/index.php?id=0,1,0,0,1,0
Also have you tried a Google Image search on "torchwood toshiko"? Some of those images might lead to more good images.
