Drain Plug - Metric Thread???

I'm a first time flipper and have a nasty challenge that I hope you can help with. We replaced an original cast iron tub in this 1966 built home, tiled the enclosure and as we were installing the final items (i.e. shower head, knobs, etc.) we discovered the new drain plug (and any alternatives we could find) didn't fit. We double-checked and triple-checked our options from local suppliers and although we have no problem matching the size, none of the replacements have matching threads. My plumber surmises that the threads on the old drain plug may be metric.

If we can't find this part our only option, at the moment, is to cut through the wall from under the kitchen cabinets and replace the overflow and drain. Not a pleasant thought when the right part would do the trick in 2 minutes. Anyway, I was wondering if anyone had experienced and solved this challenge. Also, I wondered if there was some "go-to" plumbing supply business that offers hard to find or out of production items. I'm told what I need is a 1 3/8", fine thread drain plug with non-standard threads.

Any help will be much appreciated.

drains

There were many "odd ball" thread sizes in those days. Crane had one which was not to today's standards, but there is an adapter for it. If you can identify the o.d. and thread pitch, one of the specialty companies, such as Plumbmaster, should be able to locate a bushing.

drains

HJ,
Thank you for your encouraging comments. I did contact Plumbmaster, but they wouldn't help me because I'm not operating a plumbing business (I'm an owner / builder doing a flip) and they only sell to the trade. They did suggest going to danco.com and also offered names of two plumbing companies in my area. I've zipped off an e-mail to danco and will contact the plumbing companies later today to see if either of them would be willing to help. Again, your comments were helpful and I'll provide an update as this issue moves toward resolution.

Redwood flips the coin and it says change out the waste and overflow...
Your looking for a hen's tooth...