How to get 3D molecular structures for 270 compounds?
There are a few resources that can get you what you want, but you'll probably want to consider some level of scripting automation. A search for 270 molecules isn't enormous, but doing it by hand would still be tedious.


PubChem: Run by the NIH, it offers many types of searching, and 3D coordinates for most compounds.
ChemSpider: Run by the RSC, it allows searching by name and has 3D structures for many (if not most) compounds. I'm less sure on quality, since they don't clarify how they generate their 3D coordinates.
NIH Chemical Resolver: Run by the NIH as well, it converts between different representations, including name to 3D structure.


Each offers automation tools, including Python interfaces called PubChemPy, ChemSpiPy, and CIRpy.

My choice would probably be the chemical resolver, partly because the access is very simple to automate:

https://cactus.nci.nih.gov/chemical/structure/"structure identifier"/"representation"

So you'd set up a URL like: https://cactus.nci.nih.gov/chemical/structure/aspirin/sdf?get3d=true

The result will be in SD format, but it's easy to convert that to XYZ or Gaussian files with Open Babel.