Harris Cyclery in West Newton, Massachusetts is one good source. It was formerly managed by the late Sheldon Brown, the guru of fixed-gear conversions since long before fixies became hip. Sheldon's articles on conversions of old bikes are still a great source of advice.
Are the wheels on the bike now trashed or unuseable? If not, you could replace only the rear wheel, unless you care about having the wheels match. In fact, if the wheels are good, you can build it with the existing wheels, as a bike of that vintage has a freewheel hub, which has the same thread used for a fixed cog. Many sources strongly discourage this (it's sometimes called a "suicide hub") because the cog can unthread with extreme back pressure (it lacks the reverse-thread lockring of a true track/FG hub). But if you're using brakes and avoid hard skip-stopping, it's one way to simplify and save $, and it can be done safely with those caveats (I've ridden thousands of miles on conversions done that way).
I'm very satisfied with my Wabi SS bike, everything is very quality, great customer service from Richard. I would buy a pair of thier already built wheels, great looks, weight, durability, were quite true out of the box and have been durable. I'm 190lbs riding the standard wheelset, they now have a lightweight wheelset, good prices too.
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