I've put together a simple channel vocoder here: https://hoxtonowl.com/patch-library/patch/Channel_Vocoder/
It's completely untested! I've not had a chance to try it with audio yet.
If you want to give it a go, I suggest putting the blocksize up to 512 or 1024.
It doesn't do overlapping windows which might be necessary for a decent result. It does however compute in less than 40% CPU so there's room to improve.