Lightroom should put photos in trash when you delete them from disk using Lightroom, *iff* the device supports trash. If you delete a photo and it's not in the trash, then the device does not support trash, or Lightroom has a bug (or there was a cockpit error) - which is it?
To answer your question more specifically - if you deleted from disk in Lightroom and not in trash, there is no way to see them - they're "demolecularized and dissipated" (permanently deleted). ok, you could use forensic data recovery techniques if desperate..
I thought that if I deleted a photo both from a collection AND my hard drive, it would show up in my mac's trash, but it doesn't ...
Is there any way to see your trashed photos?
Maybe you could start by relating exactly what you did (deleting what file from where in Lightroom that was stored on which disk), what you expected and we know the result you got.