Spent enormous time looking for these parts, and can not even find how they are called. Tried mouser, digikey, farnell, arrow. The best I found is "crystal insulator (thermal)" which is not what I am looking for.
By the way, last time I obtained them by desoldering old SMD quartz crystal assemblies.
Edit: yes, I want my THT crystal mounted to look this way, being held by this assembly