From what references I was able to find, both pillars and windows for those sorts of building are super simple, to the point where pre-fabbed ones are probably unlikely.
Pillars appear to be literally just plain untapered cylinders with an equally plain square final. Similar in general proportion to the big fancy temple columns, but that's it. Windows are just simple boxes, sometimes with a basic "t" munton, usually without. Get some dowel and precut basswood squares from the craft store, and you're set for the pillars. Some plain balsa or basswood wood strips for the window frames.
I'm not very knowledgeable about roman architecture though.
Did find this blog post though:
https://lockupyoursheep.blogspot.com/2014/05/28mm-roman-villa-and-ludus.htmlDude made a villa out of laser cut wood. Reading between the lines, I think he designed and cut it himself rather than it being from a commercial kit though.