In the past, if you had a Section and lair number it was possible to contact the cemetery office, which is located in the Western Necropolis cemetery. Several year ago I did that and arranged a date and time and someone took me to the location of the lair. Sadly there was no stone. However, I am sure I read somewhere, maybe on this forum, that they had stopped providing that service.
Do you have the Section and Lair number ?
You can sometimes locate a lair or at least the approx. location using the map
https://www.glasgowfamilyhistory.org.uk/ExploreRecords/Documents/St%20Kentigerns%20Cemetery%20Plan.pdf . If you find the section, and have a close look at some headstones down near their base or on the sides. You sometimes find the lair reference number is inscribed. They are usually in sequence, tho not always, so you can narrow down the location within the section. Even if no stone exists, you can get a reasonable fix on where the lair is.
Andrew