Wallingford Bike stocks 12, 13, and 16.5mm Brooks rivets. The 13 and 16.5 mm ones seem reasonably priced at $10 per 10. They appear only to have 4 of the 12mm rivets in stock at present:
http://www.wallbike.com/
I've purchased small repair bits and new and used saddles from Bill Laine and have been very pleased with the service.
Charlie Young Honey Brook, PA
Don asked:
> Does anyone know of an affordable non-brooks source for brass rivets
> in like sizes, e.g. 8 mm, 12 mm, 16 mm ??
>
> - Don Gillies
> San Diego, CA