You've pretty well covered the case options, etc. With DW out of the picture and given the fact that Spinmaster worked on DW cases and dials, those two are gone.
There is 'Son of Phong' who sells parts on ebay- world_time_inc_online is his store- he's got a few dials and other parts.
So like you say, the cartel watches are really the only way to go unless you spend big on Phong stuff, also there's MQ over in Saigon, expensive and always a challenge buying from someone in Vietnam.
M2M is your other option- keep your eyes open.