Did you have Lightroom make a 2nd copy when you imported them. If not, then in the future, you should.
Also, Lightroom does not pull your photo files into itself, it merely makes a note where the files are on disk. So, the files should still be somewhere on disk, wherever they were copied to when you imported them, or wherever you moved them to after copy/import (even if that's the trash can).
If you permanently deleted your photo files after importing, then (never do that again, and) your only recourse is to use disk recovery software - on the card, if possible, or on you hard disk(s) where the photo files used to be.
As an absolute LAST RESORT, you can recover the previews you see in Lr as jpeg files - let me/us know if it comes to that.
It sounds as though you may have had the card reader specified as the destination drive during the import (yes, it is possible to do that), so as soon as the card was ejected then Lightroom can no longer see the image files. If this is correct, if you haven't reformatted the card then the pictures should still be on there. In which case, re-insert the card, start Lightroom and the images should be available again. If so, you should be able to drag the folder of images from the card to your usual folder structure using the Folders Panel.