Hi Chris,
Thanks for your response. I have used both Xenu and Screaming Frog before, and they are great for searching a whole site within your niche where every broken link / missing resource is an opportunity. This is probably an easier thing to explain using an example:
We do work for a chain of care homes. If I go to, say www.carehomes.co.uk and check for missing links, I know that all the results will be an opportunity to make contact and build a relationship with a webmaster in the care home niche. So there's no need to filter these, but rather just to work my way through the list trying to build as many valuable new contacts as possible.
But if I run a missing links search on the BBC, it may bring back hundreds or thousands of results, but only one or two will be related to the care homes industry and therefore present an opportunity to reach out. So that's the aspect I'm enquiring about - going to a site that covers a range of topics and quickly finding opportunities within that relate to my niche.