You have not mentioned your city in the question. Toyota Etios Doesn't come in CNG variant. So there are less chances of that, you can get a CNG kit at company's authorized service center. However you can ask a service station near by you, for a CNG kit. To get the details of your nearest Toyota service station, please visit the link below-
You can also contact other authorized service stations, which provides an authorized CNG kit. But we don't recommend you for aftermarket kit.
lpg kits are approved via govt of india. UNITAX is best bec its cheaper kit and isi approved only cost 9000rs from 900cc to 1500cc vahicals + 2500rs extra for government approval on your RC.
u can install lpg kit in any patrol car.
etios is just a entry level sedan in Australia ppl do lpg conversation on almost every high end cars like ford falcon holden commodor toyota camery etc. bec lpg is cheaper.
and 100% taxis run on lpg I had a toyota Rav4 fitted with Lpg converson kit.
Both Toyota Etios and Swift Dzire are good options, while the Etios has space, Swift certainly has a powerful engine, better interiors and after sales services. The Dzire also enjoys better resale value.