While AISI 1018 is normally available in many places within India, there are not many manufacturers of chromoly pipes of small thickness. Though few of them may promise to supply it, the properties of those steels vary much with chromoly. Hence as of now it should be a wise option to purchase it from outside India.
Quality being the advantage of buying from outside, there is a disadvantage of additional shipping cost. Normally the shipping costs are almost equal to the cost of your purchase. Hence if you decide upon chromoly, start saving your money.
There are many companies outside India where you can find chromoly of size close to your requirement. Since the standards differ, you get thickness only in the order of 0.035″ , .049″, 0.058″, 0.065″, 0.083″, 0.095″ and 0.120″. A casuist would choose a thickness greater than your requirement to be on the safer side.
Following are the websites address of few chromoly dealers:
All these vendors gives us the rough estimate of cost of purchase while the shipping estimate is also provided in the first link.