Need a foot support brace like this one for my broken foot. Any shop in Chiang Mai that might stock it? Thanks. 

Maybe try one of the bigger pharmacies. They may be able to order for you.

 

Or try Lazada. 

https://www.lazada.co.th/products/afo-brace-orthosis-splint-facture-recovery-fit-i2635838890-s9462471355.html?spm=a2o4m.searchlist.list.115.46c14a57u7hNVL&search=1

 

HTH