Protocol documents such as RFCs and Microsoft's Technical Documents are implementation-independent descriptions of behavior and data that define (in detail) the requirements that all implementations of a protocol must follow.
AUTOSAR ( https://www.autosar.org - see Tab "Standards") has a whole pool of requirements specifications (organized in moddules). SWS stands for SoftWare Specification.
check my work where you can find basic requirements for 17 quality features which I used to build a reference architecture in pervasive computing. Chapter 3 and 4 will be very useful for you
Thesis Pervasive Computing Reference Architecture from a Software E...
My page has publications which are excerpts of the thesis containing simplified details.
Please let me know if you need support or collaboration
OK. Getting some types of documents will be difficult, because any companies view these documents as proprietary. Most of the research on requirements has been done in Scandinavia. One possible source is public projects. I would start locally, where your school is known. You may want to look at Agile backlogs. Simply, start contacting development organizations and expect a lot of rejection and no responses.