I don't think upper Indus Basin includes Nepal. Whole Nepal falls under Ganges River Basin. You can use APHRODITE data ( https://www.chikyu.ac.jp/precip/english/ ) as it is gridded climate dataset prepared from observed observations. This data covers whole monsoon asia and it is free.
In the situation where you find it difficult to access a gauge / weather station in any location, you can retrieve climatic data from gridded simulated/re-analysis data sources. Examples of these sources are ;