Hello Pat,
You can buy them from MLCS, but beware that their catalog prices them at $17.95, but the website lists them for $4.00 more. I don't know why. The positive side is they have free shipping. The bars can also be purchased from Eagle America for $17.95, but they charge for shipping. Brass set up bars are used to determine exact heights of the router bits from the table top, as well as other measurements. They are unaffected by moisture and retain their dimension. They also do not damage your bits (much) if you accidently hit them with the bar.
JoeZ