Yes, the v3.33 microprocessor is still available from B&O under the part number in my previous post, and it will work in the earlier BS3500 models (without powerlink socket), but there is no MCL support in this firmware, so the 3500 be ML only from that point onwards - but I'm guessing this is unlikely to be a problem if you're wanting it for N.RADIO/N.MUSIC support.
I've mainly installed this module where there was a ML gateway in the setup as 3.33 supports the ML gateway (as well as N.RADIO and N.MUSIC).
The part is unfortunately more expensive than the older 2.x microprocessor was though.
Martin.
CORRECTION: current version is 3.34, not 3.33 (but the part number is still the same).