Update Fall 2022:  The factory has not been able to supply me with more of the Type D chargers but I've been able to source the Charger X which is perhaps an even nicer solution than the Charger D and it's the same price.  https://rolleiflex.us/products/charger-x-for-rolleiflex-6000-series-batteries-with-nimh-and-nicad-cells

I have also tested a charger produced by an enterprising Rollei user. It's working okay with NiMH packs, but it's a bit more fiddly than the Charger X. I had trouble sliding in one or two batteries,  and I found it didn't charge NiCad packs as well as the X.  But one advantage - it's less expensive and works with NiMH packs.  I am not stocking them currently however you can order one here: Version2 charger for Rollei 

No longer available:

C-Type charger has been out of production for some time, and I'm happy to announce that the factory has come up with a new charger solution for the batteries.  These work with the NiMH celled batteries and will charge the ones with higher capacity cells all the way up.   I'm stocking the ones with power supplies with US plugs but have a few protoypes with Euro plugs so if you need one just e-mail me.

https://rolleiflex.us/products/rolleiflex-type-d-charger-for-6000-series-batteries-with-nimh-cells