Is there any repository where one can find standard applets introduced in Global Platform or ETSI or other standards (e.g. Security Domain, Contactless Registry Service, etc.) ???
Unfortunately not. Usually these applets (Security Domains, USIM, RAM/RFM OTA, ...) require some native integration in the operating system because the standard JavaCard API is not sufficient here, e.g. think of the necessary Milenage or TUAK algorithm needed for the network authentication of an USIM - there is no JavaCard cryptographic support for this (OK, Milenage could leverage the AES as primitive).
Hence all the implementations are custom implementations by the vendors. Because SIMs/eUICCs are also in control of a mobile network operator there is also no use case why this could be useful to an individual developer which can another reason why nothing is available as OS here.