So, the first question is what kind of relationship "counts" as being part of the Raj? If purely administrative structures are enough, then Aden and the British territories in the Persian Gulf can be added to your list as they were governed as subdivisions of the Raj until 1937 and 1947, respectively. British Somaliland and Singapore were also both governed as part of India for short periods, so it isn't impossible for those colonies administration to simply never be reorganized. Of course, they were both separated for reasons so you'd need a reason for the British to ignore the causes for separating the colonies IOTL. However, it also seems to me that in part people mean something closer to "feels like part of Britain's Indian empire" than "formally an administrative subdivision of British India". That of course is a much taller order.
Sri Lanka is relatively simple to achieve. Just have the initial period of Company rule after the capture of the island go better than IOTL so the creation of the Crown Colony is avoided and Sri Lanka follows the rest of the Company territories. Similarly, from some quick googling it seems the Maldives weren't never governed as part of India either, but due to the way the protectorate was established, so it seems simple enough to simply place them under India administratively. Nepal also seems simple enough with fairly minor tweaks to their earlier history; perhaps the British conquer Nepal in the 1814-1816 war, or Nepal sides with the Sepoys in the Mutiny and is conquered in the aftermath. I don't know enough about Bhutan and Sikkim to comment in detail on them, but I can't imagine it being hard to find a scenario.
The other obvious areas for expansion are regions bordering India which would, presumably, have been incorporated into that structure like Afghanistan, Tibet, further expansion in Persia and the Gulf, and other border regions like parts of Siam. Maybe Malaya on the outside, as I believe the Company was responsible for the early involvement in the Malayan states, and as noted Singapore was part of India for a time.
Other areas, like British territories in East Africa seem much harder to create a plausible scenario for, as to my understanding their colonization was driven by British interests and forces from southern and central africa, not India. That being the case it is hard to imagine how and why those regions would be placed under India. But perhaps an earlier conflict with Oman could lead to Britain taking control of their east african territories earlier and driven by India.
