If you know where one is (ie at your home base), return and click on it to teleport yourself to the other. When you were searching, did you hold the alt key down while backtracking, to help spot it?
If you lost both teleporter stones, you can wait until you reach the part of the game where you get them back from the imp, or as a last resort, download the inventory files to get another set;
Lost Items - guide and directory of inventory filesIf you make a new save, or a copy of your latest save, and follow the instructions in the lost items post, you can find where your own teleporter stones are.
When you load the save with the downloaded files, drop one teleporter stone on the ground without touching or moving the other. Clicking on the dropped stone should teleport you to one of your stones, as long as it is on the ground. If that doesn't help, reload the save, then drop the other teleporter stone. Once you know where one of your stones are, you can load you original save, and just delete the duplicate you were using the inventory file trick with.
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