"Cometh the hour, cometh the man" is a sort of proverbial statement suggesting that - whatever trouble happens - some sort of 'saviour' will appear to sort it out. It's not about teaching specifically, I know, but it fits the bill well enough. Click here for a site with information on the source of that one.
If you put "teacher will appear" into the Google search-slot, you'll get over 38,000 hits many of them with the exact words you offered yourself. So, it seems your wording is correct. Perhaps one or other of the sites will offer a source.
I think it's a zen proverb and the meaning is that your teachers are already all around you. What is missing is your realisation that you do not know. Once you make yourself ready to accept tuition then you will recognise the potential sources of instruction.