Given that you are a web firm, would you not be able to put together something which meets your needs specifically in a reasonable amount of time, and something that only gets used internally?
If you don't want to go down the full system development route, you could look at a customer relationship management (CRM) solution. There's loads out there, some free (SugarCRM and vTiger as examples) which can be customised either through adding custom fields which you need, or you can do development into them and build in the functionality that you need.
There's paid offerings too, such as salesforce.com, but that can get expensive quickly with add-ons, or OpenCRM; which isn't open source, despite what you might expect from the name. Full disclosure: I am a former employee of OpenCRM so my view on the system will most likely be biased. I know the latter system will work for what you need, and can be customised to have extra fields to hold the information you need (it's used internally within OpenCRM for similar purposes). This can be done by system admins or by your account manager and their team with relative ease.
Aside from the general system route, there's another less high-tech route (and massively more insecure) where you store the information in a spreadsheet which the relevant people have access too, and search the sheet when you need certain information.