I am sorry but the E4418A, E4418A, EPM-441 and EPM-442 have been discontinued for a long time and are no longer in support life. Our policy is that even after the end of support life we still performa best effort basis to try to help you out. Unfortunately I can't find the information you are looking for.
Many of the components stayed the same during the varioius versions of the power meter. You might check out the E4419B power meter's service guide. There may be enough information there to help you get what you need.
Also the Agilent find a part web page
http://www.home.agilent.com/myagilent/faces/fapHomePage.jspx?_afrLoop=1773491933836000&_afrWindowMode=0&_afrWindowId=null#%40%3F_afrWindowId%3Dnull%26_afrLoop%3D1773491933836000%26_afrWindowMode%3D0%26_adf.ctrl-state%3Duulmdq7li_9 may also be able to help you. Enter in the Product Number E4419A in the Product section. It will show a long list of parts which may include the part yu are looking for.
Good Luck
