A city with only 1 type of core available? Impossible! You surely can get an old PC PSU. There is a big ferrite core (EE or EI) in it. With about 2 mm air gap it is much better than the crappy yellow iron powder, or air cored inductor.
Or you can use the core of the High Voltage trafo of any CRT TV or monitor. Etc... there must be some tons of it in any town for free.
Air core is OK for high power only if you use litze wire or you make it very big.
Approximately L=n*A/h*mu0
A is the core cross-section, h is gap height, mu0 is permeability of vacuum (0.00000125). Everything is in SI unit.
BUT:
You must define saturation current requirement!
Approximately Isat=h*250(A/mm)/n
For example A=200mm^2, 1 mm gap height, 14 turn is about 50 uH, with Isat=17 A.
For 30 A you need h=3 mm and 25 turns, but this gap height has a relatively strong fringing flux, wires have to be kept away from it.
thimios, you can find here > Switch Mode Power Supply Circuit SG3525 IR2110 900W SMPS - Electronics Projects Circuits