We have estimated Intra-industry trade (IIT) indices as well as marginal intra-industry trade in various working papers such as Growth in India’s Intra-Industry Trade, it is University of Mumbai, Department Working Paper and others are ISFIRE Working Paper Series,such as AN EXAMINATION OF DETERMINANTS OF INDIA’S INTRA-INDUSTRY TRADE and Foreign Direct Investment and Intra-Industry Trade in India’s Manufacturing Sector: A Causal Relationship and
Be careful because RCA is different from Intra-industry trade (IIT). RCA reveals comparative advantages of an economy compared to an other geographic area (or compared to its own structure of export) while IIT measures the share of intra-industry trade on overall trade. To estimates IIT ratios, you have a lot of indexes from classic Grubel and Lloyd to corrected one. Have a look here to choice the best index for you (in attached file). You can also have a look to my latest working paper where I use a corrected Grubel and Lloyd (https://ideas.repec.org/p/grt/wpegrt/2015-28.html).
Concerning you question about Stata, I do not find a package to calculate it. You should make your own calculation. E-mail me if you want me to send you my do-file on the calculation of IIT.