Symbian is dead - and I don't think any 3rd party developers are in the least bit bothered - they're development software was as buggy as Windows Mobile, as hard to use as Android and with more restrictions than Apple's iOS.
However if you try poking around Symbian/Nokia related forums you may find some hobbyists who first started programming via the Symbian OS - they're the most likely to be interested in developing something in the same way that some are still developing new Z80 and C64 software