Hi Billy,
As well as being Common on plumage, now is also not a time when there's many (if any) Green Sands about - they are passage migrants in Britain (with a small handfull wintering, mainly down south), and just now, they're all on the breeding grounds in Scandinavia etc. By contrast, Common Sandpipers breed here, so are (as their name suggests!) reasonably common at this time of year.
Your best chance of Green Sands is in a month or two, when they start to head back from Scandinavia. They start to reappear in early July, peak in late July, then trail off through August into early September, then just the few wintering birds after that. But even in late July, they're still fairly scarce in western Scotland, they'll be easier to find if you head across east to e.g. Lothian or Borders.
Michael