I answered a question on another mailing list and thought I should post the results here, too. Here are some sources for 151 bcd rings -
1. Campagnolo, Sugino, and Shimano (Dura Ace) all offered 151 bcd rings at one point, ending in the late 60's. You can often find slightly used Sugino and Shimano rings on ebay for very low prices, some are in 1/8th and some are 3/32nd. NOS rings of this size often sell for $100+, which leads us to other cheaper alternatives ....
2. There are at least 4 custom chainring makers in the world and they can make you a ring. This includes the mythical 43T 151 bcd ring that nobody ever stocked as a production item. The sources for custom-made rings are :
a. Japan. CT Custom Chainring, but they may be closed by now.
http://velo-orange.blogspot.com/
List member Peter Brueggeman (4peebee@peterbrueggeman.com) has purchased a 151 bcd 43T ring from this outfit.
Imho they specialize in french styled rings, specifically, Stronglight 63 and 3-arm weirdo stronglight and simplex patterns.
b. U.K. Highpath Engineering.
http://www.highpath.net/
Probably the most expensive option, they serve the time trial and HPV markets, providing full-custom chainrings.
c. Australia. Probably the lowest-cost option. Cycle Underground.
http://cycleunderground.com.au/
They have tooled up to produce a 3mm ring as cheaply as $50 (s/h extra.)
d. USA. Boone makes titanium rings in 94, 110, and 130 bcd. They serve the mountain-bike market. I never saw them advertise 151 bcd, but if they are making custom titanium rings, retooling for 151 bcd might be possible, and a titanium 151 ring might just last forever...
http://www.boonerings.com/
- Don Gillies
San Diego, CA, USA