Fletchling - along with any other Pokemon - can not be obtained originally or regularly (normal encounter) with it's hidden ability. But, there are other ways of receiving one apart from the Friend Safari.
First, horde battles are a excellent strategy on encountering one with it's hidden ability. However, fletchling does not appear in hordes. In this case you would need to breed, trade, or receive.
When breeding, there is a 60% chance to receive a Pokemon with it's hidden ability when breed with a male species of the same offspring family or egg group - likelier with their compatible parent.
Trading is a good method because you're able to ask for a Pokemon and view one to see if it's hidden ability is viable within it.
Receiving Pokemon is a good strategy. What I mean by that are event Pokemon etc.. All Pokemon received from:
1) Pokemon Global Link, Pokemon Dream World, or Global Link Promotion will 100% have its hidden ability.
2) Pokemon in OR/AS encountered using the DexNav has a slight chance to have it's hidden ability.
3) Certain event Pokemon will have their hidden ability - slight/likely chance
4) Pokemon received from hacked system (eg. powersave) will have next to or 100% hidden ability.
There are various ways to receive one, but each may take time. Good Luck! Hope I helped! :)