I also know of no such reference. Lets not forget however, that most of these systems (FPDS, CPARS, PPIRS, FAPIIS, SAM, etc) are interrelated, though they may be managed by different entities (GSA, NAVSEA, etc.). First, when placing an order against a GSA schedule look the vendor up in GSA e-library. For instance, if you search Booz Alen Hamilton, you will see that they have numerous GSA FSS contracts. Many of those are under different DUNS numbers. When you look up your vendor in GSA e-library be sure to find the particular corresponding contract, select the vendor and copy the DUNS number under which the contract was awarded. Next go to SAM and search by DUNS only. You will find the correct corresponding CAGE to that DUNS. If you do this when awarding TOs/DOs against a GSA FSS (and I assure you it only takes a minute or two), you shouldn't run into your particular problem anymore.