Thanks to Victor Muñoz, radare2 now has support of the algorithm he developed, capable of finding expanded AES keys with /Ca command. It searches from current seek position up to the search.distance limit, or until end of file is reached. You can interrupt current search by pressing Ctrl-C. For example, to look for AES keys in physical memory of your system:
$ sudo r2 /dev/mem
[0x00000000]> /Ca
0 AES keys found