I have yet to see any Borax, I see from the table that it is a surface ore. I'll give it a go again later today.
As for plaster, here in the UK all our plaster is made using Gypsum (it also doubles as a fertiliser),and there is no shortage of it, maybe this could be added as a surface or shallow ore, and plentiful, just so people can create mortar to build, there is always a portion of the playerbase who arent that interested in progression, they much rather make nice bases etc.