I've killed one anaconda at a HI RES so far on 1.3 as well. It was the first wanted AI to spawn when I arrived at the RES and I have yet to see one since. I have been doing missions lately and all of the anacondas seem to be at strong signal sources.
I know one day Anaconda's will return to the RES; but it isn't a a bad thing not having them around. I'm getting a lot of bounties worth over 200k from Dropships and Pythons and up to ~180k for the Clippers. Anaconda's at low combat rank are not worth much...