Sharma and Pukkala (1990) volumes are widely used in Volume and biomass estimation of Nepalese tree species. However, there are some research papers which you can find them using google search. I may have scanned version of Sharma and Pukkala with me (I have to dig my hard drive on this), this reference, in my opinion is outdated. I would suggest you few works from outside of Nepal are:
Article Improved allometric models to estimate the aboveground bioma...
Article Tre allometry and improved estimation of carbon stocks and b...
Updated generalized biomass equations for North American tree species (Article Updated generalized biomass equations for North American tree species
Comprehensive database of diameter-based biomass regressions for North American tree species
@Mukti Subedi, thanks a lot. I got sharma and pukkala 1990 report as scan copy from Pukkala research gate. Thanks for new references which I didn't had before.