These seem to change quite frequently.
Here in Phoenix the feds have a number of encrypted talkgroups on the PRWN system. No idea who they are or what they are talking about, since their encrypted.
P25 is becoming alot more commonly used by the feds on their VHF channels, if you have a BC250D or better, search in the 162-174 range and you'll hear them. Also check 416-420 Mhz - anything that isn't part of the AFB system could be USBP... you'll have to listen to it to see.