This page details the steps outlined on the Accessing PMIP3-CMIP5 data page. The PMIP3 and the CMIP5 databases overlap and data access instructions that you can find on the official CMIP5 web site also apply for PMIP3
The variables requested for CMIP5 (and PMIP3) are detailed in the standard_output document.
You should download the xls or pdf version of the document and find out the standard names of the variables you need
The common PMIP3-CMIP5 and the PMIP3-specific data are distributed through the ESGF (Earth System Grid Federation) network. This is basically a world-wide collection of:
Each P2P FE will let you search the content of all the other nodes, so you only need to pick up the P2P FE that is closest to you. You can start with one of the P2P below, and look at the Peer Nodes list on the left to check which P2P is closer