George Nelson 2202B Clock Battery Conversion  

Check your local hobby places (like Michael's in the USA) that sells quartz battery movement to get a sense of what fits with the existing clock hands holes you have or contact a local clock repairman (if they still exist in your area), maybe they might still have an older battery operated movement that fits with the same period Howard Miller clock.
You can also do this by yourself if you know what you have to do and where to find vintage battery operated clock mechanisms. Use caution that you are not adding additional damage to the clock hands hole if you must do this yourself. Good Luck.
Also your clock will only be worth as a functional decorative vintage object and will not command the same value as a vintage version with all original working mechanism if you decide to resell.

Some might consider it sacrilegious, harvesting parts for repairs from damaged or unrestorable pieces. Keep your eyes open for some late models 1970s and 1980s Howard Miler (and other makes too) modern clocks that in terms of design merits, unmemorable/uninspired.
They do show up, sometimes for next to nothing and other times with inflated price tags. The quartz movement as long as it is still functioning properly will most likely fit your clock.

Why not buy a synchron 1rpm clock motor? They can still be found.
http://www.ebay.com/itm/Vtg-GEORGE-NELSON-HOWARD-MILLER-ELECTRIC-SYNCHRO...

tell me how, exactly, that hexagonal clock is lacking in design merits