This is likely what your "org link" refers to. Many Bengali literature enthusiasts upload scanned copies of out-of-print pulp fiction here. Search for "Swapan Kumar Samagra" or "Nalini Kanta."
Some older Bengali detective stories have been digitized as part of cultural preservation projects. inspectornalinikantas02 complete bengali org link
If the digital hunt fails, the is widely available in physical form through publishers in College Street, Kolkata. Buying the collected volumes is the only way to ensure you have the "complete" series without missing chapters or poor-quality scans. This is likely what your "org link" refers to