G3XBM (Roger): Weather boots for coax plugs?

I'm looking for what I believe are called "weather boots" to slide over the end of PL259 and BNC coax plugs to help protect them up the mast from water ingress. I guess it is still necessary to add a smear of silicone grease. There are such items for Sky dish F connectors (see eBay item 251296277220) but I have not yet found a source for the common 50 ohm plugs.

Anyone know where such rubber/PVC boots can be obtained please?