Before you buy:

Most of the seatpost for US track bike are in 27.2mm size. But better to double check and buy accordingly.

You can use lower sizes but you need a shim then, remember that not every shim is available on the market but you can do your own with a soda can; the common shim is 1.0mm so you can use a seat-post 26.2mm but I would not use a 27mm seat-post because is impossible to find a 0.2mm shim.

When you buy a seat-post check the saddle size also, and distance between rails because not every saddle can fit a seat-post. For instance Nitto Jaguar seatposts (japanese imported version) iare very narrow and fits good with Kashimax but not Brooks (unless you force the rails.)

Brands to search for:

Miche, Nitto, Campagnolo Record (also some Athena are nice), Vintage Sake, Sugino, Kalloy and Gipiemme.