How do I find the proper toilet seat for an antique toilet with an irregular bolt spread?

I am trying to find toilet seats for two toilets that are part of a house that was built in Boston around the turn of the century. The seats were made by the Dalton-Ingersoll Co., Boston USA (which is now out of business) and called Burmuh No. 1

A normal bolt spread on a toilet is 5 1/2" or 10" but this toilet has different specs. It has an outer set of holes with are around 3/4 inch in diameter and around 6 5/8" (from the inside of the hole) apart. This makes the holes around 7 1/2-5/8" inches apart.

An inner set of holes, which look to me to be drilled after the fact, at 1/2" in diameter and approx. 4 5/8" apart (making it close to 5 1/8-1/4" inches apart from the center).

Overall, the shape of the toilet is fairly standard round shape. Any thoughts on how I should proceed or where to look? Thank you for your help, I have pictures if that helps. Thanks again.

Some seats will have floating brackets, and can be moved to the right pattern. Have you tried the Home Depot, you could probably special order one. If it's this difficult to find, when you do find one, order a couple of them, and store one. Another option is to go to an older Mom, & Pop hardware store, they might have one buried on a shelf. Good Luck, I hope this works.

Yes, they have changed the sizing in this country because of manditory tank size regulations. Try looking for what you want on line in Canada.

There are companies that specialize in old/weird stuff like this. You'll have to check out handyman magazines and contractors & plumbers & suppliers for names.
Good luck.

i don't know where you live. there are stores that specialize in salvaged materials from old houses. my suggestion would be to start there. check the yellow pages in your phone book or check on line. good luck

Many reproduction oak seats have a bar across the back.
which allows the hinges to slide to accomodate variying mounting hole locations.
Hope that helps.