Finding a mainspring for an unknown calibre? Buren 12s 15j

Attempting a service on an old Fasco / Buren 12s 15j. On disassembly come to find that the mainspring is broken (last component to come out, naturally...). I am currently challenged by not knowing the movement calibre, although given the obscurity of the make even knowing this may not help all that much.

I can take measurements of the old mainspring & barrel diameter, but I don't have any idea for what strength I should be looking for.

Width 6thou / 0.152mm
Height 68thou / 1.727mm
Barrel 614thou / 15.59mm
Hook-end



Any suggestions from the OF community for what & where to look would be appreciated.

Cheers

You need to messure through the whole mainspring and then you can find a replacement here. You can also find a good explanation abou mainspringmessurements and types

https://www.cousinsuk.com/category/filter/mainsprings-by-size-search-watch-pocket

Thanks to all, that's helpful.