Can you still purchase the boards?
Where do you suggest getting spare boards?
Where can we get the old boards repaired?
Most modern (i.e. more complex) Otis control boards are not widely repaired by third parties, and as you point out, some parts like OVF30 drives are now obsoleted by Otis. There are a few companies out there that offer services refurbishing Otis drives. For other PCBs you might find some door control and fixture PCBs here and there, but the main control boards like RCB II (OCSS) and the MCSS or LMCSS are generally not being repaired. You might get lucky finding some second hand "as-is" PCBs out there as jobs are modernized, but I expect most non-OEM companies probably retain them for their own spare parts supply to avoid paying the crazy prices that Unitec (Otis' own spare parts company for non-Otis customers) charges.
Doing a Google search, Master Elevator Parts in Long Island City NY seem to have some Otis PCBs from the E411 era, but I am not affiliated with them and have not purchased anything from them.
Good luck!
With used main control boards the key issue is whether the company supplying them has the capability of thoroughly testing them
Overall the 411-MMS is solid controller but unfortunately with boards becoming obsolete it will be time to start considering a modernization.