Is there a standard Ethernet Connector?
RJ45 is an 8-position 8-contact jack, so every plain RJ45 connector that has a different number of contacts is not an RJ45. But many connectors have contacts for additional features like shielding or built-in indicator LEDs.

Ethernet requires tranformers between the RJ45 connections and the driver chip. These transformers can be built into the connector, in which case the hybrid connector-transformer can have more PCB contact pins. Note that the specs (turn ratio's) of these transformers depend on the particular driver chip.

Sorry, there is no standard ethernet connector part. If you are concerned about long-term availability choose a part that has pin-compatible equivalents from at least one alternate manufacturer, and check whether the big suppliers (mouser, digikey, farnell, etc.) all stock these parts.