Thanks @colorado.rob I started with Keysight and they said they didn't have any and that the part was obsolete; the part number for the U1252A is U1251-64404 (note: the last digit is different from the one you mentioned which is for the 'B' model). However, they look identical (although it's hard to tell precisely given the angle of the photo). I'll see if I can buy one and see if it fits. Even for the one you mentioned, I didn't see a purchase option when logged into the Keysight website.