What should be the order of specific conductance (κ) of floride, chloride and bromide ions?
ppm is ambiguous quantity, it can be v/v, w/v,w/w,n/n. 

By other words, all 1 ppm very probably is not the same molar concentration, unless it is n/n ppm, relating itself to the molar amount of the solution.

$\Lambda = \kappa /c$ is correct, but $c$ must be the molar concentration.

$$\Lambda[\pu{Sm^2mol^-1}]=\frac{M[\pu{g/mol}]}{c[\pu{ppm as g/m^3}]}\cdot \kappa[\pu{S/m}]$$