That's an interesting tasker given to you.

Unfortunately a complete search of DAU's material and an internet search did not find any exhisting list of all instances when a determination and finding (D&F) is required. But you are in luck! The Acquisition.gov website has a FANTASTIC search engine with logic and filter options to choose from. WIthin a matter of seconds a search revealed 72 instances of the phrase "determination and finding" in the FAR spread over 14 different FAR parts and 68 instances of the same spread over 15 different DFARS parts.

Please be aware that many of those will be discussing the same D&F. Also be aware that there are a few instances where the FAR and DFARS use the acronym "D&F" in lieu of the complete phrase, but those are becoming more and more rare with each technical amendment of the FAR/DFARS. That should jump start your search.

For more guidance on when a D&F should be used rather than a memorandum for file; see FAR subpart 1.7. Note that at FAR 1.700 it states that "Requirements for specific types of D&F’s can be found with the appropriate subject matter." Which means, a D&F is required when the FAR states that one is (it will not be vague about that fact). Whereas a memorandum for the contract file should be done when circumstances neccesitate one (e.g. a contract deliverable fails inspection, etc.) or shall be done when the FAR/DFARS states something like "document the contract file..." without using the phrase determination and finding or D&F.

For a real quick demonstration: see the language at the FAR 11.103(e) compared with the language at FAR 25.1001(a)(2)(iii).