Lots of Edison spark plugs show up on eBay, but most are not for Model T. Which one(s) are? I gather #13 is one. Are there others?
Edison #14 and #13 both fit a Model T. Edison 14s are the same physical size as Champion X. Edison 13s are physically larger, and harder to find, but have the same 1/2 inch pipe thread that fits a Model T. Edison 13s also have dual ground electrodes.
Edison 13 vs. 14:
13's are the Edison "split fire" ? Cool.
You might try contacting this gentleman via snail mail if you want some Edison plugs. Last time I contacted him, he was out of Edison 14s, but he still had some Edison 13s (at what he implied was a steep price, not compatible with Mister Thrifty guidelines).
You send him a letter (he doesn't use email) telling him what you are looking for. He sends you a letter back telling you what he has and the price. You then send him back a letter with a list of what you want to buy and a check for the amount. He then sends you a box with the plugs.
Plug tough guy McKinsey only had the one Edison 13, l posted photo of it on this forum. While l was mining through his collection l came across a NOS 14 that needed re-blueing; he may still have that if he can find it.
He does have email and phone but only gives it out if he thinks you're a serious guy.