A bookstore I've regularly visited over the last couple of decades is the 150+ year old Higginbothams on Mount Road, Madras (Chennai).
(pic source link: wikipedia)
My first ORMS textbook: 'Linear Programming and Network Flows' by Bazaraa, Jarvis, and Sherali was purchased here. In recent years, finding the latest ORMS books here has become tedious. The Chennai Metro rail construction has adversely impacted the parking area in front. Yesterday's search spanned the entire second floor, and ORMS/Business Analytics books were found in the following sections: Management (Management Science books), Operational Management (OM, Supply Chain), Statistics (a slew of Intro2ORMS books, probability models, queuing theory), Linear Algebra (Linear Programming), Computer Science (computational complexity, graph theory, combinatorics), ... Perhaps this situation is a reflection of the field of ORMS itself. It's been a multidisciplinary area since the beginning.
Sapna book house in Bangalore has a good collection of computer science oriented material.
SBH once boasted of a huge collection of technical books, and it's still a pretty decent place to look for books relating to business analytics, data mining, and machine learning.
Gangarams is another well-known book store in Bangalore.
I've found very few ORMS books here in the past, and I plan to skip it this time around.
Off late, flipkart.com, the Amazon-like online bookstore offers a massive assortment of books, including ORMS titles. It ships only to Indian addresses currently, accepts credit cards, and offers free home delivery within 2-7 business days. Despite these benefits, online shopping denies one the simple joy of a leisurely enumeration search in the afternoon, wading thru stacks of old, dusty tomes in search of that one hidden gem. In a totally random location at Higginbothams was a copy of 'Optimization for Machine Learning'.