If you have no luck do it yourself with a few cheap tools that you will use many times.
Buy a micrometer, digital ones are less than £10 from a tool shop or ebay and sometimes Lidl, that will get you the diameter of the nipple.
Buy an inexpensive thread guage Ftead Gauge Link
You now have the thread diameter and the thread pitch from a nipple you have already removed from a caliper and the threaded length of the nipple.
You can then search for the exact spec of the nipple rather than hoping someone sends you the correct nipple.
Both items will come in handy and there are plenty thread charts on the net to identify the thread from you info.