If you are looking for a copper tube with an outer diameter of 3.75mm for use in
VRF piping, you may be able to find it at a HVAC supply store or plumbing supply store that specializes in heating, ventilation, and air conditioning (HVAC) equipment. Alternatively, you could try searching for it online on websites that specialize in HVAC parts or on general online marketplaces. It may also be helpful to consult with a licensed HVAC technician or plumber to ensure you are purchasing the correct size and type of tubing for your specific needs.