Where could I find a MATLAB implementation of TCAS algorithms and simulation?
My research work deals with collision avoidance of a multi-UAV scenario in a small airspace.
Otherwise, they did release quite a bit of details in reports. You'll probably end up rebuilding it from their logic.
If you are planning to build your own implementation and you are looking for the pseudo code of TCAS then buy a copy of the TCAS II MOPS. It includes the algorithm description.
You can find it as RTCA document DO-185B, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance Systems II (TCAS II).
If the size of the airspace is small and you're just looking for collision avoidance between UAV's you'd probably be better off using FLARM, which is used by gliders. There is a variant of it called "UAS Electronic ID". The standard is open and available on request.