Well, in case anyone's interested in following up on this further, using the La Trobe University on-line search engine, a search for the term mahāpurisalakkhaṇ (truncated to allow for various inflections) leads to 77 (BJT) record hits, at least 65 of which are in the Pali Canon.  Here's the first page of the search results (with links to the subsequent pages as well):  http://www.chaf.lib.latrobe.edu.au/dcd/pitikaresults.php?title=&start;=60&to;=70&searchstring;=mahāpurisalakkhaṇ .  
Of course, this is by no means a straightforward indicator of how many discourses actually reference this term (nor what this term means in the context of various suttas) since multiple records can be part of a single sutta.  (Similarly, this is not a clear reflection of the total number of times that this term appears in the Pali literature as a single record could have multiple instances of the term and their might be other ways of formulating this phrase not addressed by the above truncated compound term, etc.).  
FWIW, a quick review of these results (potentially suggestive of the distribution of this term in the various nikayas) shows 40 hits in the Digha Nikaya, 15 in the Majjhima Nikaya, none in the Samyutta Nikaya, 3 in the Anguttara Nikaya, and 7 in the "canonical" Khuddaka Nikaya (mostly in the Suttanipata), 5 in the paracanonical KN words (e.g., Netti, Peta), one in the Abhidhamma's Kathavatthu, once in the Visuddhimagga, and 5 times in the Pali histories.  If nothing else, this distribution perhaps suggests that suttas identified by Peter and myself might possibly be (among?) the core texts. -)
With metta,  (talk)