Depends what you mean by Airplane shops. If you are looking at every kind of aviation merchandise then sorry, there are none. Certified and Final.
But if you are looking for bookshops with plenty of Aviation stuff, there's one in DEL. Its called the English Book Store and is located in Connaught Place. The selection is very poor but it does have an aviation section mostly with technical stuff. They also keep some poorly crafted airplane models.
If you are looking for airplane models etc., you can get Revell and AirFix type models of various scales at Hobby Centre (Again Connaught Place/DEL and close to the English Book Store). For aeromodelling you can try Hobby Centre (Russel Street, CCU). If you want to see trash dished out as IAF souvenirs, try the Air Force Museum at Palam. Be warned, Mirages look like Jaguars look like MiG-21s look like Sukhois and none actually look like a real plane.
Sarfaroshi kii tamannaa ab hamaare dil mein hai, Dekhnaa hai zor kitnaa baazu-e-qaatil mein hai