What a thrill to see some interest in this topic. Perusing ACIMs I found a number of Regiments still mention stable belts in the Regimental Standing Orders. Among them are, in no particular order:
LdSH(RC)
Communications and Electronics Branch
RHFC
48th Highlanders
The Blackwatch (RHC)
KOCR
Lorne Scots
The LdSH, RHC, and RHFC actually include pictures of the belt in wear with various orders of dress, which I found interesting.
Further to this, The RCR used to mention them in the 1960's Regimental Standing Orders which prompted me to write a brief article about their usage in The Regiment's history. For those interested the article can be found here
https://milart.blog/2018/06/10/stabl...dian-regiment/