try this search:

http://shop.ebay.com/i.html?_from=R40&_trksid=m570.l1313&_nkw=dillon+dynamometer&_sacat=See-All-Categories

You probably want one in the 1000 to 3000 lbs capacity range. I have one of the electronic ones, purchased for a different need. I have used it to measure running rigging stress among other things. The electronic ones are interesting: a machined but solid aluminum frame has shackled attached to each end, and an electronic strain gage measures the distortion in the frame.